In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element(CAFE) model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions(UDFs) to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also investigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy(SEM). The experimental results showed that four major types of microstructures were formed: dendritic, equiaxed, mixed, and multi-droplet microstructures. The simulated results and the available experimental data are in good agreement. In this study, the microstructure evolution of rapidly solid ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element (CAFE) model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions (UDFs) to simulate the microstructure of gas-atomized particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy (SEM) The experimental results showed that four major types of mi The simulated results and the available experimental data are in good agreement.