3D cement printing is an emerging technology that can construct building elements without formwork, which has broad application prospects in the field of constructing non-linear and complex building structures. However, the high-quality printing and molding of nonlinear structure has become one of the bottleneck technologies restricting the development of 3D building printing. In this paper, variable radian 3D printing nozzle is firstly developed to verify the controllability of extruded concrete material based on self-developed 3D building printer. Then, variable radian forming theory is presented and used to evaluate the mechanism material fracture and accumulation, and improve the molding quality of nonlinear structure. Finally, simulation analysis and experiments are designed to explore the controllable mechanism of variable radian molding and verify the consistency between the experimental results and the theoretical analysis. The research results can promote the application of 3D printing in the construction industry, and provide support for the utilization of building resources and green buildings.