As transition metal silicides have been successfully synthesized, the study of the combination of transition metal and silicon is another effective way to investigate the properties of silicide. We recover novel structures of two silicides: MSi (M = Tc, Re). The structures phase are ɛ−FeSi phase (P213) and CsCl phase (Pm3m). Using the Cambridge Serial Total Energy Package (CASTEP) code, we researched the mechanical, electronic and optical properties of MSi (M = Tc, Re) under 0 GPa and 100 GPa. It is found that each structure is dynamically and mechanically stable at 0 GPa, and the Vickers hardness values show that all of them belong to soft materials. Besides, both the P213-MSi and Pm3m-MSi have metallic characters under 0 GPa and 100 GPa. For the reflectivity in the optical properties, it can be observed that the atom and pressure have obvious influence on the reflectivity of Pm3m-MSi, while only the pressure has obvious influence on the reflectivity of P213-MSi. We hope our work will provide some help to the experimental work on the technologically material.