Cobalt-based superalloy DZ40M sample is prepared by laser additive manufacturing method and its microstructure is studied. The microstructure and mechanical properties of the alloy under different heat treatments are compared. Results show that the dendrites size of DZ40M microstructure obtained by the laser additive manufacturing method is finer than the traditional directional solidification structure, and the tensile strength and plasticity are improved in different degrees. Solution treatment under 1280 ℃ can make the primary carbide achieve full solid solution and new eutectic structure appears. Then after 950 ℃ or 1020 ℃ aging treatment, the secondary carbides are obtained. The samples after aging treatment show better mechanical properties. Especially, 1280 ℃/4 h+1020 ℃/12 h heat treatment system can improve the tensile strength at room temperature and keep the maximum degree of ductility of the deposition state sample.