This study aimed to improve the sintering quality of biomass composite powder by using walnut shell and copolyester hot melt adhesive (Co-PES) powders as the main raw materials to prepare the walnut shell/Co-PES composite (WSPC) powder for selective laser sintering (SLS). An orthogonal experimental design of five factors and four levels was adopted to optimize the process parameters for the SLS experiment. Moreover, through range analysis, the influences of laser power, preheating temperature, scanning speed, layer thickness, and scan spacing on the quality of WSPC were also studied. In addition, the synthesis weighted scoring method was used to determine the optimum process parameters. The results showed that the WSPC part quality was optimum when the laser power was 12 W, the scanning speed was 2000 mm/s, layer thickness was 0.15 mm, scan spacing was 0.2 mm, and preheating temperature was 80 °C.