If the reality of the impact phenomena in the field of collision becomes well understood, that will open the path for the research of safety and security in a considerable manner. Therefore, the dynamic behaviors of the occupant and the belt system should be sought through very careful analysis. In this work, we use the computer simulation technique by dynamics of multibody systems and FEM continuum model. The relation between the occupant''s motion and all the potential correlating phenomena in the belt system is to be cleared. And eventually, the simulation will lead to advanced seat belt systems.A response for the impact would be divided into two phases: impulsive response immediately after collision and the subsequent quasi-static response. The former is essentially conceived to compose of stress wave, and the latter is elastoplastic response. The response for the impact, therefore, will be observed as follows: the generation and propagation of stress waves within the webbing and the acceleration response within the occupant. The former response should be integrated as belt force F, and the latter as head G''s, etc.In order to prove that phenomena, model of occupants'' seat belt system in frontal collision is to be examined. For observing of the propagation phenomena of the stress wave, FE belt model has been introduced. The behaviors of the stress wave are characterized in the forms of the propagation of Von Mieses stress. From the time evolution, it can be seen to increase like a stepwise- wave, which is a result of superposition of the reflection on the traveling wave. Eventually, the responses immediately after collision have been proved to compose of the stepwise-wave.A key point for controlling the impulsive response immediately after collision would be found in the process of artificially building analogous phenomena to the propagation and reflection of the waves. We are taking a positive approach in order to improve the two factors: the restraint capacity for occupant and the efficiency of belt system. More specifically: Improvement in occupant protection techniques (Decrease of peak Gs); and Reduction of the impulsive load on the seat belt systems (Decrease of peak Fs).