The core task of Air Traffic Control is to ensure flight safety and to improve operation efficiency. In process of approaching, many factors can cause the aircraft not flight strictly in accordance with the planned route. In the same, because of the traditional trajectory clustering analysis did not looked the aircraft approaching as a process to consider and it lack of time information, in order to simulate more realistic, a method of spatial clustering with time windows was proposed in this paper. And a reasonable approach standard center trajectory in every minute was extracted. Then using biharmonic spline interpolation method, we calculate the entire airspace approach procedure trajectory distribution probability. The results show that this method is fast and effective, more in line with the actual situation of air traffic command and control.