Hi Lifeng.
If I understood you correctly, you have read the Migration workbench manual and the available documentation.
What you could do in your situation is upload the input text fle to the server (either using EMIGALL - Convert migration file itself, or by transaction CG3Z or any other method you have). Once you do that, you should convert that file to a migration file (again, EMIGALL - Convert migration file).
From that point on, you should probably do distributed import, for which you have step-by-step guide here: EMIGALL - Scheduling Distributed Import Job (EMIGMASSRUN) procedure.
Hope this helps.
Marko