Abstract: In order to reasonably evaluate the number of berths of a bus bay stop,a probability calculation method is proposed based on observed data.This method supposes that demand exceeds supply for bus berths in each unit time, combines with the classical capacity calculation model and considers the delay when buses change lane leaving a bus stop. Moreover,this method analyzes the relationship between berth demand and traffic capacity,from the point view of supply and demand balance of bus berths.The Second Changjiang River Bridge Stop in Wuhan is selected as a study case.Accord-ing to the situation of this bus stop,the upper limit value of bus queue overflow probability is set as 15%.The results show that the probability that demand exceeds supply of this bus stop in one unit time (1 min)is more than 15%.By in-creasing the number of bus berths using this proposed method,the capacit of bus stops can meet the traffic demands (p<15%).This method will be very helpful for berths design of one bus bay stop.