According to the textual research on the historical earthquake records about Hongyapu earthquake in 1609 and field surveying result of castle and wall in Hongyapu,Qingshuipu and Suzhou,it is considered that the extremely seismic area of the event located between Hongyazi and Jinfosi,the intensity was Ⅹ,magnitude reached about 7.25,the direction of long axis of isoseismal lines are NWW.We also emend three incorrect records in historical data.