With the minimum mass of steel structure for bodywork as the object, beam sections and location topologies as design variables, and the stress and displacement as constraints, the optimum model is established. With the method of killing or activating elements, a high level technique in MSC. Marc, by Genetic Algorithms, a new scheme of researching structure topology optimization is proposed and the calculation procedure system is programmed. Applied the system, a steel structure of bodywork is optimized successfully. The validity and practicability of the system are certified.