do I need to apply for a visa for china, if so where is closest to Nagoya city and what prepare?

I am a Vietnamese citizent. Currently I am being as a visiting scholar at Nagoya University, Nagoya city, Japan. I have two passports, an ordinary and an official one. I have used ordinary passport for staying in Japan, my visa in Japan last one year until March 2012 and re-entry visa. In August 16th-21st, 2011 I will attend a international conference in Shanghai. Do I need to apply for Visa for China? or I can use official passport?
Many thanks for your help