The gear-alternating control regulation was first actualized at the interfluent location of on-ramps in Shanghai elevated roads, which was theoretically studied in this paper. Different traffic flow models were established for the cases with and without the alternate controlling regulation based on the Fukui-Ishibashi cellular automaton traffic model. With the models, the traffic behavior at the interfluent location of on-ramp was investigated and some results were obtained. When there are many inflowing vehicles on the elevated road and ramp, the traffic situation on the elevated road with the controlling regulation is much better than that without it; when there are less inflowing vehicles, the elevated road situation on the whole remains the same in the two cases.