<dx:ASPxGridView ID="gridView" runat="server" ClientInstanceName="gvResults" Width="550px"
                AutoGenerateColumns="True" KeyFieldName="OrderID" DataSourceID="AccessDataSource1">
</dx:ASPxGridView>
<asp:AccessDataSource ID="AccessDataSource1" runat="server" DataFile="~/App_Data/nwind.mdb"
                SelectCommand="SELECT * FROM [Orders]"></asp:AccessDataSource>

<script type="text/javascript">
        window.__OriginalDXUpdateRowCellsHandler = ASPxClientTableFixedColumnsHelper.prototype.ChangeCellsVisibility;
        ASPxClientTableFixedColumnsHelper.prototype.ChangeCellsVisibility = function(row, startIndex, endIndex, display) {
            if((row.cells.length == 0) || (row.cells[0].getAttribute("ci") == null))
                window.__OriginalDXUpdateRowCellsHandler(row, startIndex, endIndex - 1, display); // base call
            else {
                //custom processing
                for(var i = startIndex; i <= endIndex; i++) {
                    var cell = FindCellWithColumnIndex(row, i);
                    if(cell != null)
                        cell.style.display = display;
                }
            }
        };

        function FindCellWithColumnIndex(row, colIndex) {
            for(var i = 0; i < row.cells.length; i++) {
                if(row.cells[i].getAttribute("ci") == colIndex)
                    return row.cells[i];
            }
            return null;
        }
=================================   

    protected void Page_Load(object sender, EventArgs e)  {
        if (!(IsPostBack || IsCallback))
            gridView.DataBind();

        new ASPxGridViewCellMerger(gridView);

        gridView.Columns[0].FixedStyle = GridViewColumnFixedStyle.Left;
        gridView.Columns[1].FixedStyle = GridViewColumnFixedStyle.Left;

        gridView.Columns[0].CellStyle.BackColor = Color.FromArgb(0xEE, 0xEE, 0xEE);
        gridView.Columns[1].CellStyle.BackColor = Color.FromArgb(0xEE, 0xEE, 0xEE);

        gridView.Settings.ShowHorizontalScrollBar = true;
    }

===========CellMerger.cs=====================

using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using DevExpress.Web.ASPxGridView;
using System.Collections.Generic;

public class ASPxGridViewCellMerger {
    ASPxGridView grid;
    Dictionary<GridViewDataColumn, TableCell> mergedCells = new Dictionary<GridViewDataColumn, TableCell>();
    Dictionary<TableCell, int> cellRowSpans = new Dictionary<TableCell, int>();

    public ASPxGridViewCellMerger(ASPxGridView grid) {
        this.grid = grid;
        Grid.HtmlRowCreated += new ASPxGridViewTableRowEventHandler(grid_HtmlRowCreated);
        Grid.HtmlDataCellPrepared += new ASPxGridViewTableDataCellEventHandler(grid_HtmlDataCellPrepared);
    }

    public ASPxGridView Grid { get { return grid; } }
    void grid_HtmlDataCellPrepared(object sender, ASPxGridViewTableDataCellEventArgs e) {
        //add the attribute that will be used to find which column the cell belongs to
        e.Cell.Attributes.Add("ci", e.DataColumn.VisibleIndex.ToString());
        
        if (cellRowSpans.ContainsKey(e.Cell)) {
            e.Cell.RowSpan = cellRowSpans[e.Cell];
        }
    }
    void grid_HtmlRowCreated(object sender, ASPxGridViewTableRowEventArgs e) {
        if (Grid.GetRowLevel(e.VisibleIndex) != Grid.GroupCount) return;
        for (int i = e.Row.Cells.Count - 1; i >= 0; i--) {
            DevExpress.Web.ASPxGridView.Rendering.GridViewTableDataCell dataCell = e.Row.Cells[i] as DevExpress.Web.ASPxGridView.Rendering.GridViewTableDataCell;
            if (dataCell != null) {
                MergeCells(dataCell.DataColumn, e.VisibleIndex, dataCell);
            }
        }
    }

    void MergeCells(GridViewDataColumn column, int visibleIndex, TableCell cell) {
        bool isNextTheSame = IsNextRowHasSameData(column, visibleIndex);
        if (isNextTheSame) {
            if (!mergedCells.ContainsKey(column)) {
                mergedCells[column] = cell;
            }
        }
        if (IsPrevRowHasSameData(column, visibleIndex)) {
            ((TableRow)cell.Parent).Cells.Remove(cell);
            if (mergedCells.ContainsKey(column)) {
                TableCell mergedCell = mergedCells[column];
                if (!cellRowSpans.ContainsKey(mergedCell)) {
                    cellRowSpans[mergedCell] = 1;
                }
                cellRowSpans[mergedCell] = cellRowSpans[mergedCell] + 1;
            }
        }
        if (!isNextTheSame) {
            mergedCells.Remove(column);
        }
    }
    bool IsNextRowHasSameData(GridViewDataColumn column, int visibleIndex) {
        //is it the last visible row
        if (visibleIndex >= Grid.VisibleRowCount - 1)
            return false;

        return IsSameData(column.FieldName, visibleIndex, visibleIndex + 1);
    }
    bool IsPrevRowHasSameData(GridViewDataColumn column, int visibleIndex) {
        ASPxGridView grid = column.Grid;
        //is it the first visible row
        if (visibleIndex <= Grid.VisibleStartIndex)
            return false;

        return IsSameData(column.FieldName, visibleIndex, visibleIndex - 1);
    }
    bool IsSameData(string fieldName, int visibleIndex1, int visibleIndex2) {
        // is it a group row?
        if (Grid.GetRowLevel(visibleIndex2) != Grid.GroupCount)
            return false;

        return object.Equals(Grid.GetRowValues(visibleIndex1, fieldName), Grid.GetRowValues(visibleIndex2, fieldName));
    }
}

ASPxGridView-单元格合并