呃，是因为你的默认加载行数的问题

http://www.foxtable.com/help/topics/1813.htm

谢谢老师，我就是默认不加载多行的。代码修改在这个样子就解决了 ，多加了红色代码

Dim Cols1() As String = {"第一列","第二列","第三列"}
Dim Cols2() As String = {"第一列","第二列","第三列"}
Dim dr2 As DataRow
dim r as datarow
For Each dr1 As DataRow In DataTables("AA").Select("")
    dr2= DataTables("BB").SQLFind("第一列 = \'" & dr1("第一列") & "\'")
    If dr2 Is Nothing Then
        r = DataTables("BB").AddNew()
        For i As Integer = 0 To Cols1.Length -1
            r(Cols2(i)) = dr1(Cols1(i))
            r.Save()
        Next
    Else
        dr2("第二列")=dr1("第二列")
        dr2.Save()
    End If
Next

For Each dr As DataRow In DataTables("BB").DataRows
dr.load
Next