In subway system, a lot of transponder are paved on the track to assist the positioning. While the positioning of tramcars is different from the subway because of the positioning and the cost, the tramcars system usually adopt the method of combination of a few transponders or beacons, the speed sensors and GPS to position comprehensively. Therefore, the positioning precision of GPS is one of the most important conditions of positioning veracity. Due to the influence of the satellite offset, the GPS receiver offset and the route of transmission, the precision of GPS positioning decreased. In order to improve the precision of GPS positioning, Kalman filtering method was employed to best estimate the position of tramcars. The target track in different situations such as uniform motion, uniformly accelerated motion and variable accelerated motion were simulated and the results showed that the positioning error was greatly reduced by adopting the Kalman filtering algorithm. From the results of simulation, Kalman filtering method could reduce the impact of noise and greatly improve the precision of positioning.