Based on the vulnerability analysis and the hazard analysis，a numerical calculation method for risk probability of bridge exposed to fires caused by vehicles was developed． According to the statistical data of vehicle fire accidents，the probability density function of maxim heat release rate was estimated using the principle of maxi- mum entropy． A vulnerability analysis method of bridge member based on RSM-MCS was proposed，and a vulner- ability analysis method of structural system was given by the research about structural system，correlation and dam- age criterion of system． The risk probability of a simply supported beam bridge under fires caused by vehicles was provided to illustrate the method． The results show that the suggested method can effectively evaluate the fire resist- ance of a bridge．