The official information ：

You can create lsmw for data migration as follows (using session method):

Example for xk01 (create vendor) 
Initially there will be 20 steps but after processing 1 step it will reduced to14 for session method.

1. TCode : LSMW. 
2. Enter Project name, sub project name and object name. 
    Execute. 
3. Maintain object attributes. 
    Execute 
    select Batch Input recording  
    goto->Recording overview 
    create 
    recording name. 
    enter transaction code. 
    start recording 
    do recording as per ur choice. 
    save + back. 
    enter recording name in lsmw screen. 
    save + back

Now there will be 14 steps. 
2. MAINTAIN SOURCE STRUCTURES. 
    Here you have  to enter the name of internal table. 
    display change 
    create  
    save + back

3. MAINTAIN SOURCE FIELDS. 
    display change 
    select structure 
    source_fields->copy fields. 
    a dialogue window will come . 
    select -> from data file 
    apply source fields 
    enter No. of fields  
    length of fields 
    attach file 
    save + back

4. MAINTAIN STRUCTURE RELATIONS 
    display change 
    save + back

5. MAINTAN FIELD MAPPING & CONVERSION RULE 
    display change 
    click on source field, select exact field from structue andenter 
    repeat these steps for all fields. 
    save+back

6. MAINTAIN FIXED VALUES, TRANSACTION, USER DEFINED 
    execute  
    save + back

7. SPECIFY FILES. 
    display change 
    click on legacy data 
    attah flat file 
    give description 
    select tabulatore  
    enter 
    save + back

8. ASSIGN FILE  
    execute  
    display  change 
    save + back

9. IMPORT DATA. 
    execute  
    display  change 
    save + back

10. DISPLAY IMPORTED DATA 
      enter ok, it willl show records only. 
      back

11. CONVERT DATA 
      execute  
      display  change 
      save + back

12. DISPLAY CONVERTED DATA 
      execute  
      display  change 
      save + back

13. CREATE BATCH INPUT SESSION 
      tick keep batch input folder  
      F8 
      back

14. RUN BATCH INPUTSESSION. 
      sm35 will come 
      Object name will be shown here  
      select object & process 

LSMW-摘自SAP官网