Abstract:  Under condition that the cycle time of traffic light switches is relative short, the optimal control problem of traffic light at a single intersection is discussed. The objective is to minimize the expectation of queue length at the end of Kth cycle with K being a given integer. Given the queue length of vehicles from each direction at the initial moment, a queuing model is developed to describe this problem. Then, an efficient algorithm is proposed to solve it. A numerical example is used to verify the effectiveness of the proposed method.