Ph.D in history, nankai university. Professor and Director of history department of nankai university. Committee member of the history teaching steering of the education ministry. President of the Chinese tang history society and chairman of the department of history of tsinghua university. Professor and doctoral supervisor of history department of tsinghua university. Vice President of Chinese foreign relations association. He was selected as professor by the national personnel department “A million talents project” (1997) and tsinghua university “985 Talent program”(2003), "Yangtze scholar" (2006). He is mainly devoted to the study of Chinese ancient history, the history of Chinese and western cultural exchanges and historiography theories, especially in the history of the sui and tang dynasties. Achievements have been made in the history of Chinese and western cultural exchanges.