At present, the passage rule of intersection is that care in each of two oppositeroads can go simultaneously during the green light period. It can clearly be seen, the cars go-ing ahead in one road conflict with those turning left in the other, making the traffic efficiencydrop down. There is a new rule executed in some main routes in Shanghai, that is each roadindependently attains the green light in turn. In the paper, the model of cellular automata isused to simulate the carrying out of these two rules. The results illustrate the new rule isbetter than the old one, when care run above a certain speed.