To ensure a safe，aesthetic，and lightweight building envelope，an ultra-high performance concrete （UHPC） building envelope and its node connection mode were proposed based on topological optimization and modular composition.Firstly，the UHPC building envelope was optimized by using the method of minimizing structural compliance subjected to given material volume constraints，and the mechanical performance before and after optimization was compared.The modular design was adopted，and the optimization result of the most unfavorable stress area in the model was taken as the basic configuration unit.Then，UHPC tenon and mortise nodes were proposed，which could be simply assembled into modules.By considering the weak mechanical performance of nodes，the finite element analysis （FEA） of the nodes was carried out，and the nodes were compared with the traditional bolt-steel plate nodes.The results show that the UHPC building envelope based on topological optimization and modular composition not only ensures high stiffness and bearing performance but also reduces the volume by around 35%.Compared with the bolt-steel plate node，the tenon and mortise node in this paper has advantages in mechanical performance，so it can achieve the same strength as the traditional bolt-steel plate node.In order to achieve better results，the inward camber of the key teeth of the UHPC tenon and mortise node should not be greater than 60°，and the camber angle should not be less than 90°.