Abstract: A three-dimensional microstructure simulation method for gas pores was proposed based on a coupled thermal flow model of cellular automata and powder scale. A cellular automaton model was constructed using MATLAB to simulate the two-dimensional microstructure of titanium alloy Ti-6Al-4V produced by additive manufacturing, and the simulation results were consistent with the experimental results. Through the joint simulation of FLOW-3D and EDEM software, the finite volume method was used to simulate the three-dimensional multi-pass powder bed melting process, and the temperature field information was obtained.Expanding the cellular automata model to a three-dimensional scale, the obtained temperature field data was imported into the cellular automata model to numerically simulate the microstructure at the hole location, and the microstructure distribution was obtained. The method helps to construct a multi-scale model for metal additive manufacturing process design, defect characterization, performance evaluation, and it is used for predicting information such as grain size, defect distribution and fatigue life.