Abstract: Bus accessibility evaluates the difficulty of travel over the transit system .However ,the simulation on the influencing factors to bus accessibility has never been adequately studied by far .A simulation method of bus accessibility based on Monte Carlo is proposed ,where two influencing factors ,road congestion and departure interval ,are analyzed . First ,the accessibility measurement using isochrones is set forth .Second ,the travel process is divided into four parts :waiting for buses ,travel on road ,arriving at the stops and transfer .Time models of each sub-process are built ;therefore the Monte Carlo simulation model is constructed .Finally ,an ideal network on a checkerboard pattern road network is constructed and its simulation is performed under different road congestion conditions and departure intervals .The simu-lation results show greater increase in accessibility under weak force .