In accordance with the requirements of the side impact test of C_NCAP, in the early phase of a new car body in white (BIW) development, effective side crashworthiness load paths are found through topology optimization.And the base design is defined according to topology optimization result, benchmark and manufacture requires.Then the SFE-Concept implicit parametric BIW model is built.The shape, section size, position and gauge of BIW parts which influence side crashworthiness are defined as optimization design variables.Side crashworthiness and global stiffness performance approximation models are created through the design of experiment (DOE).Analysis and optimization time are controlled through optimizing approximation model.A detail design is completed according to performance multidisciplinary optimization (MDO) and lightweight MDO results.Through optimization not only side crashworthiness and global stiffness performance satisfy design targets but BIW mass reduces maximally.The design parameters percent contribution and main effect plots are obtained through analysis of variance (ANOVA).The rules between design parameters and performances (mass, global stiffness and passive safety) are in evidence according to percent contribution and main effect plots.Topology optimization and MDO are successfully applied in new BIW architecture development work.The study on the topology optimization and MDO explorations in the platform/modular vehicle product development is ongoing.