持有綠卡，但是已經離開美國八年沒有回去過，所以估計綠卡已經作廢，現在準備去北京申請B2簽證，想請問一下放棄綠卡是不是必須要填報Form I-407才能去申請B2簽證?
-Correct. After the I-407 is approved, provide the approval notice (i.e., the approved I-407) for the B2 visa interview.
See this link for abandonment of green card in China:
Abandonment of Status (Form I-407) - U.S. Embassy & Consulates in China
