Abstract: With the rapid development of metal additive manufacturing technology, laser selective melting technology(SLM) is widely used in the production of titanium alloy closed impeller because of its advantages of large forming freedom, high precision and low surface roughness. In the additive manufacturing process, the inside of the closed impeller is usually unable to self-form, and a support structure needs to be added.In order to design optimal internal support structure of a closed impeller, Simufact Additive software was used to simulate the deformation and residual stress during the forming process of the closed impeller.Based on the simulation results, the mechanical properties of the support body were regulated by adjusting the type, size, distribution and process parameters of the support, and the relationship between the support strength and porosity was analyzed by means of microscopic CT.The results show that the surface roughness of the optimized inner cavity of the closed impeller after support removal is reduced from 528 μm of the original block support to 13 μm, and the fatigue strength is increased by 84.8%.