This paper deals with investigation to determine optimum vehicle deceleration in order to reduce occupant injuries for frontal impact of vehicle at the primary design phase. The first purpose of this investigation is to calculate occupant chest deceleration under one degree of freedom spring and mass model by using convolution integral when various frontal crash impact of vehicle occurs. Next we developed and found out how to reduce maximum chest deceleration by analyzing unit impulse response

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... nd influence curve of chest deceleration sensitivity by changing small range of vehicle deceleration fluctuation. Further we also conducted three patterns of vehicle deceleration curve sled test for frontal impact under the Hybrid III dummy restrained by the rigid seat and seatbelt. As the result, this paper reports that this method can be estimated, as for the relative comparison of occupant chest deceleration when the frontal crash impact of vehicle changes even though the real world occupant safety restraint system of seatbelt is equipped.