[Purposes] In order to meet the customized requirements of low energy-consumption and light-weight elevator car, a variation design framework of modular car structure based on "Internet + " is constructed. [Methods] First of all, under the B/S architecture, Vue technology was used to develop user-defined design data acquisition front-end to obtain customized design requirements, and Springboot technology was used to develop modular structure variation design back-end. A Web framework for front-end separation was built, which can realize bidirectional binding of front-end and back-end data. Secondly, a topology optimization design method for high-specific stiffness considering stress constraints was embedded in the back end. The strength and volume fraction of the car structure was considered as user-defined constraints，and the maximum stiffness of the car modular structure was optimized as the optimization goal. The moving asymptotic optimization algorithm was used as the solver to drive the rapid customized variation design of the lightweight car modular structure. Then, the heavyside function was introduced into the optimization method to ensure that the design results have clear geometric boundaries. Finally, taking a certain type of backpack elevator car frame as an example, the geometric and mechanical boundary parameters of the car structure were set in the user-defined interface to carry out the variation design of the innovative lightweight car frame structure, and the finite element simulation analysis was carried out. [Findings] Under the premise of given design requirements, the structural variation process was stable and convergent, and the geometric boundary of the designed structure was clear. Under the same mechanical boundary conditions and meeting the 2 times minimum safety factor of the material, the mass of the designed car frame structure reduced 16.09% comparing with the original structure.The structural deformation was ensured to meet the practical application requirements, and the specific stiffness was significantly improved, which verified the effectiveness of the structural variation design framework established in this paper. [Conclusions] The proposed design framework can improve the specific stiffness of the structure under the premise of ensuring the strength of the structure, which can be effectively applied to the rapid customized design of the lightweight elevator car modular structure. It can shorten the design cycle of the car modular structure, and enrich the design means of the car modular structure.