Abstract: Buffeting response spectrum of long-span bridges is calculated by coupled spectrum analysis in the frequency domain,and the time history of structural responses induced by buffeting is simulated by trigonometric sery composition approach.While a large amount of samples about buffeting time history are generated with Monte Carlo simulation technique,it is relatively easier to numerically solve the probability of first passage failure of long-span bridges.Two numerical examples referring to buffeting deflections of the Jiangyin Suspension Bridge and the Shanghai Yangpu Cable-stayed Bridge have been considered.The numerical results are also compared with those obtained from three semi-analytical approaches,namely Poisson process,Poisson envelope process and Markov process.The results show that by considering the background component of the atmosphere turbulence,the proposed numerical method is very precise and effective,especially in the case of higher threshold values.