Well formed bulk CoCrW alloys are fabricated by selective laser melting (SLM) and the effect of the heat treatment process on the phase composition, microstructure, and microhardness of the CoCrW alloy is studied. The equilibrium phase diagram of CoCrW alloy is simulated and calculated by JMATPro software, and the X-ray diffractometer, scanning electron microscopy, and microscopic hardness tester are used to test the phase composition, microstructure, and microhardness of the CoCrW alloy before and after heat process. Results show that the original SLM sample mainly comprises γ phase and a trace amount of ε phase. After heat treatment, a large portion of γ phase is transformed into ε phase, and the lump- and strip-like precipitate phases are produced. The size of the precipitated phase at the fusion line is large under low temperature heat treatment, and it is clearly different from those of other regions. The grain boundary and grain size of the precipitated δ phase grow with the increasing heat treatment temperature. Simultaneously, the difference in the precipitated phase size at the fusion line decreases. The microhardness of the CoCrW alloy decreases after heat treatment, especially for heat treatment at 1100 ℃ followed by water cooling.