In this study, 18Ni300 maraging steel powders and micron silicon carbide (SiC) powders are sintered using selective laser melting technology. Furthermore, the effects of adding different volume fractions of SiC for roughness, microstructure, and mechanical properties are investigated. The results reveal that with the increase in SiC volume fraction, the swelling and spheroidization of the top surface are aggravated, the surface roughness and pores become larger, and the side powder adhesion is serious. Additionally, the solidification structure changes from cellular crystals to columnar crystals and then to dendrites, and the samples of hardness and tensile strength are higher than those without SiC powders. When the volume fraction of SiC powders is 0.5, the hardness and tensile strength samples are the highest, reaching 371.1 HV and 1.51 GPa, which are 7% and 54.8% higher than the sample without SiC powders, respectively. Therefore, while the addition of SiC powders increases the top surface roughness and porosity, it can transform and refine the grain, increase the dislocation density and improve mechanical properties, and then enhance the comprehensive performance of the sample.