The alloy TMW-4M3 has been developed as a novel cast and wrought alloy based on a concept of combining Ni-base and Co-base superalloys. This alloy contains higher amounts of Co and Ti than Alloy 720Li. For practical applications, it is very important to control the size and distribution of γ’ phase as an intended microstructure. However, precipitation behavior of this type of alloy greatly depends on heat treatment conditions. In this study, we made a modification to the thermodynamic database in order to obtain reasonable γ/γ’ phase boundary in the range of high Co composition. By using it, both the nucleation rate calculation based on classical nucleation theory and the microstructure evolution prediction based on the phase field method were applied to the precipitation of intragranular γ’ particles during the heat treatment process. The simulated microstructures under different temperature history conditions agree well with experiments in both the size and the morphology of γ’ precipitates.