构成SQL语句时日期直接使用是不行的，即使变量是日期型，但构成SQL语句时还是会被当成字符串处理的，要想把字符串转换称日期型数据，需要用“#”括起来，例如下面这个统计过程：

Private Sub btnOK_Click()
    Dim StartDate As Date, EndDate As Date
    Dim strSQL, strItem As String
    
    DoCmd.SetWarnings False
    DoCmd.RunSQL "Delete from tblTransSum"
    
    '统计日期
    StartDate = Nz(Me.txtStartDate)
    EndDate = Nz(Me.txtEndDate)
    If StartDate = 0 or EndDate = 0 Then
        MsgBox "请先选择日期，然后点击统计按钮！", vbCritical, "提示"
        Exit Sub
    End If
    '统计单位
    If Me.frmItem = 1 Then
        strItem = "FAbbr"
    Else
        strItem = "CAbbr"
    End If
    '统计
    strSQL = "Insert into tblTransSum (Item,ExtraFee,DeductFee,SettleFee,CExtraFee,CDeductFee,CSettleFee) Select " & strItem
    strSQL = strSQL & ",sum(ExtraFee),sum(DeductFee),sum(SettleFee),sum(CExtraFee),sum(CDeductFee),sum(CSettleFee) from tblTransport"
    strSQL = strSQL & " Where AuditState and AuditDate Between #" & StartDate & "# and #" & EndDate & "# Group by " & strItem
    DoCmd.RunSQL strSQL
    '插入一条合计
    strSQL = "Insert into tblTransSum (Item,ExtraFee,DeductFee,SettleFee,CExtraFee,CDeductFee,CSettleFee) Select '合计'"
    strSQL = strSQL & ",sum(ExtraFee),sum(DeductFee),sum(SettleFee),sum(CExtraFee),sum(CDeductFee),sum(CSettleFee) from tblTransSum"
    '刷新显示
    RequeryDataObject Me.sfrList
End Sub