持有绿卡，但是已经离开美国八年没有回去过，所以估计绿卡已经作废，现在准备去北京申请B2签证，想请问一下放弃绿卡是不是必须要填报Form I-407才能去申请B2签证?
-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
