Selective laser sintering/melting (SLS/SLM) is a rapid prototyping technique that utilizes a high-energy laser beam to bind powder particles together for solid part fabrication. Due to the presence of several factors, microstructure-based material modeling can be of significant importance for optimizing processing parameters. To date, most researchers have put their efforts on simulating the microstructure of SLM-processed component, while few attentions have been paid to investigate the evolving of microstructure during SLS. In this work, a phase-field model is proposed to simulate the microstructure evolution during the solid-state SLS process. The microstructure evolution as affected by the laser power and scanning velocity are studied. It is found that the width of sintering neck increases with the increase of laser power and the decrease of laser scanning velocity. The modeling predictions are compared with the experimental data regarding the neck width between adjacent particles. In addition, it is demonstrated that this model is capable of carrying out large-scale simulations.