The effect of different heat treatment temperatures on microstructure and fracture toughness of TC4 titanium alloy fabricated by Selective Laser Melting (SLM) was studied. The results show that the microstructure is characterized by a large number of acicular martensite α" phase and β phase. The longitudinal section is characterized by columnar crystals growing along the forming direction. The angle between the acicular martensite α" phase and the forming direction is about 45o. After heat treatment, the acicular α "phase is transformed into lamellar α phase, forming α+β lath structure. With the increase of heat treatment temperature, the α lamellar coarsened gradually, the zigzags of crack propagation path increased, and the fracture toughness gradually increased from 43.1 MPa?m1/2 to 109 MPa?m1/2。.