解决的方法就是用DataTrigger取代Trigger， 然后用Binding+Converter转换为详细非Null值。

比方：

<Style x:Key="DisableStyle" TargetType="Button">
            <Style.Triggers>
                <MultiDataTrigger>
                    <MultiDataTrigger.Conditions>
                        <Condition Binding="{Binding ElementName=ckb1, Path=IsChecked, Converter={StaticResource NullableToBooleanConverter}}" Value=http://www.mamicode.com/"true">
                        <Condition Binding="{Binding ElementName=ckb2, Path=IsChecked, Converter={StaticResource NullableToBooleanConverter}}" Value=http://www.mamicode.com/"true">
                    </MultiDataTrigger.Conditions>
                    <Setter Property="IsEnabled" Value=http://www.mamicode.com/"False">
                </MultiDataTrigger>
            </Style.Triggers>
        </Style>

NullableToBooleanConverter:

public object Convert( object value , Type targetType, object parameter, CultureInfo culture )

            Nullable<bool > isCheck = value as Nullable< bool>;

            if (null == isCheck)

                return false ;

            else

                return isCheck .Value;