I find a solution myself!
We need a Common Dialog control in the form.

* Use SelPrint of RichTextbox control
* CommonDialog Control's flags

* Define constant
cdlPDReturnDC = 256
cdlPDNoPageNums = 8
cdlPDAllPages = 0
cdlPDSelection = 1

with this.parent.CommonDialog1

* Set CommonDialog Flag
.Flags = cdlPDReturnDC + cdlPDNoPageNums

If this.parent.oleRtf.SelLength = 0
.Flags = .Flags + cdlPDAllPages
Else
.Flags = .Flags + cdlPDSelection
EndIf

* Show printer prompt
.ShowPrinter
endwith

this.parent.oleRtf.SelPrint( this.parent.CommonDialog1.hDC )