In the busy airport capacity saturation phenomenon, closely spaced parallel runways implementing paired approach can effectively improve airport capacity, ease the airport runway congestion and flight delays. For ensuring safety operation of paired approach,the rear machine needs to be operated under reliable collision risk. In this paper, considering the track deflection caused by machine due to navigation error and human error, and on the basis of the situation that the front machine passes through the rear machine to approach the track, using the kinematic equation and gets paired into nearly two machine with vertical distance formula of deflection always changes, and using the Reich model launched a longitudinal collision risk assessment model, finally using MATLAB curves obtained the risk of collision with the relevant parameters, analysis of influence factors of the longitudinal collision risk.