With the rapid development of GPS and communication technology, floating car data (FCD), which is also called probe vehicle, become the essential composition of traffic information. In this paper, we propose the model based on the speed-density relationship, to estimate the vehicles between the floating cars at signalized intersection, and then we can obtain the traffic volume at intersection and other evaluation index such as queue length, which is crucial to signal optimization and control. The model is tested using SUMO simulation data. We use the error of traffic volume at intersection as the evaluation index to estimate trajectory data with penetration rates of 20% to 50%. The results indicate that the proposed model is very sensitive to penetration rates, the success rate increases with the growth of penetration rates.