sIn the early step of car development the safety is more and more important. During the car crash test, the Seat Belt is subject to large load. The buckle assembly resists the load that is applied to belt in the passive belt system. Belt system is basically important for improving the safety performance.So there are some regulations about belt system like the Seat Belt Anchorage Test which has to secure the safety during the crash of the car. Belt is flexible, so we may only consider the tension to design, but in case of buckle, if we establish the load condition in the wrong, the buckle is failed during the car crash test. We have to predict the applied load of the buckle so that we design it properly and securely. We can get the magnitude and direction of the load from basic caculation. If we apply this results in design, the buckle may fail in case of car crash. For the sake of the correct analysis, we investigated the equilibrium of the restrained system during the large load and made a model to describe this phenomena.This paper is the determination of the actual load acting on the buckle by the model to describe this phenomina and use computer simulation to examine the influence of these design load on the car crash test.