With the development of health monitoring system for the long span bridge, how to use the data effectively to give proper assessment is of vital importance in the field of the world bridge engineering. Based on the investigation of present assessment methods, through the experiences of practice engineering—Zhoushan Island Xihoumen and Jintang Bridges' health monitoring system, the authors designed a new assessment system, making comprehensive assessment of long span bridges, combining cutting-edge theory and practice, and striving to provide a scientific basis for maintenance and management.