Assuming the coming traffic flow to be stationary,a model of nonlinear programming is proposed to decide the arrangement of traffic light time of a single intersection.Its object is to ensure the least possible jam in one traffic light cycle,with some restrictions.This model fits for both the 3-leg intersections and the 4-leg intersections.Then a model for more than one intersections that are close to each other is setup.The last part of the paper discusses the stability of the two models and the ways to im...