In order to improve the safety performance of advance guide signs (AGSs) at highway exits for the di-verging area, the characteristics of the diverging area and the visual recognizing-exiting behaviors of the driver are taken into consideration, and a setting model of safe distance of AGSs, which reveals the effects of traffic flow, de-sign speed and lane number on lane-changing behaviors, is constructed based on the analysis of the computation mode of lane-changing driving distance. Then, a simulation is carried out with TSIS-CORSIM. The results indicate that, for a three-lane expressway with a design speed higher than 110km/ h, an AGS setting distance of 700m may result in minimum lane-changing number of vehicles proportionally dispersed in the diverging area, which means that the safe distance is reasonably set.