Abstract: The processes of additive manufacturing and welding are both complex processes with multiple physical field coupling, and it is difficult to directly observe the evolution of the microstructure of the molten pool by experimental methods. With the rapid development of computational material science and numerical models, it is possible to study the microstructure evolution during solidification by numerical simulation. Several commonly used microstructure simulation methods are compared and analyzed, among which the phase field method has a unique advantage in the accuracy of grain morphology simulation. The application status of phase field method in the microstructure simulation in additive manufacturing and welding fields is reviewed, and the research direction in future is prospected.