With the development of intelligent transportation technologies, the variable message signs (VMS) have been widely used in guiding and managing the dynamic traffic. It is known that cell transmission model (CTM) can well reproduce such traffic dynamics as shock waves and jams. This paper employs the CTM to study the location problem of VMS. Simulation results show that there exists an optimal VMS location to minimize the total travel time of the traffic system. How changes of route choice probabilities before and after a traffic accident affect the optimal VMS locations is also investigated and it is concluded that the VMS should be placed far from the accident site if the anticipated accident is very serious.