Microstructure has significant effects on the mechanical properties of AlSi10Mg alloy. Therefore, an in-depth understanding of microstructure evolution, such as dendrite and Al-Si eutectic, is of great significance to obtain the desirable microstructure and manage the performance of AlSi10Mg components. In the current work, an integrated dendrite and eutectic evolution model based on the cellular automaton–finite difference (CA-FD) method, taking account of solute distribution, growth kinetics, and nucleation mechanism, was established. Microstructures of the as-built selective laser melted (SLMed) samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques, and the experimental results showed that the microstructure consisted of Al grains and Al-Si eutectic networks in the individual melt pool. Dendrite growth, solute redistribution in ternary alloy and dendritic morphologies with different cooling rates were numerically investigated. In addition, the proposed model was also applied to predict the Al-Si eutectic evolution, and eutectic morphologies under eutectic undercooling in a range of 5 K to 20 K were also simulated. The simulated results indicated that dendrites were refined with the increasing of the cooling rates, and Al-Si eutectic morphology was sensitive to eutectic undercooling such that higher eutectic undercooling refined the eutectic microstructures. Model validations were performed, and the experimental results agreed well with the simulation results, indicating that the proposed model can successfully reproduce both dendrite and eutectic microstructures.