Abstract: in this paper,the natural vibsation of suspension bridge is for the first time being analysed nonlinearly by using the famous computer program A-DINA.As an exampte,the natural breguencies and associate modes of vibr-ation in the longitudinal vertical plane for Jiu-feng mountain flexible Suspe-nsion bridge is compted.The results obtained reveal that the value of natural frequency computed in the past by using linear model is smaller than that by nonlinear model,and errors are more likely to come into existence.Fu-rther more it shows that the program ADINA is also adeguate for solving the problems of dynamic response of the same structure systems.