Abstract: The feasibility of regarding multiple traffic flows as one was demonstrated by probability analysis and gap acceptance theory.On this basis,a model of average vehicle delay was established by queuing theory to find the critical traffic volume of traffic signal warrant at major-minor intersections.Then,from the viewpoint of traffic efficiency,by comparing the average vehicle delays at major-minor intersection before and after signal control,the critical volume curves of traffic signal warrant were obtained for different critical gaps of three common cross patterns at unsignalized intersection.The results may provide a theoretical basis for signal setting at major-minor intersections.