This paper presents an analysis of the nonlinear characteristics of a bridge structure and the chaos of BHM(bridge health monitoring) information. Chongqing Masangxi bridge’s BHM information is analyzed by using the max Lyapunov index with Wolf and correlation dimension with G_P algorithm. The results show:1) all of the max Lyapunov index is nonnegative ;2)the correlation dimension is non-integeral and greater than 2.These proves that the bridge structure is in the chaos. Meanwhile, with the evolution of time, the index of chaos is sensitive with status of structure system and varies in different key sections of bridge structure. These findings lay a solid foundation for the further development of bridge safety assessment and prediction when non-linear chaotic theory is utilized to analyze the bridge health monitoring information.