The 05Cr15Ni5Cu4Nb precipitation-hardening stainless steel plate is fabricated by the laser additive manufacturing technique. The microstructure, precipitated phase and mechanical property of the as-deposited, adjusted and solid solution state microstructures after aging heat treatments are analyzed, and the technology for the heating processing is optimized. The results show that the as-deposited microstructure mainly consists of epitaxial columnar grains where there are several cellular-like dendrites and residual ferrite exists in the inter-dendritic region. The tensile strength of the as-deposited state microstructure is 1128.5 MPa. After aging heat treatments, the residual ferrite is eliminated, the NbC particles and a large number of nano-sized ε-Cu phases distribute dispersedly in the martensite lath. There are significant increase in both the microhardness and the tensile strength. Compared with that of the as-deposited state microstructure, the plasticity of the direct-aging and solid-solution-aging state microstructure is lower, but the tensile strengths are 1440 MP and 1367 MPa, respectively. The adjusted state microstructure has a favorable ratio of strength and toughness, and the elongation rate and tensile strength are 16% and 1164.5 MPa, respectively.