This paper presents a trapezoid method for occupant restraint system design analysis based on occupant ride-down energy control theory.The sub-system characteristic determination of an occupant restraint system could be simplified and analyzed by a two-step trapezoid energy curve which is generated from ride-down energy control method.The parameter definitions resulted from the target two-step residual energy trapezoid analysis for some case studies were put into a numerical model for validation.Occupant responses showed very good agreements between the outcomes both from trapezoid analysis and the numerical simulation.In the concept design phase,this method could be used to give quick estimations for restraint system parameters based on occupant injury target,available vehicle crush space and interior survival space design,and provide reliable inputs for sub-restraint system design and a good reference point for the initial restraint system layout.