The complexity and concealment of the goaf environment hinder the understanding of the types of ignition sources in goaf gas explosions. Therefore, this study constructed a mechanical-electrical test system for rocks; the generation of pressure stimulated currents (PSCs) and its discharge-induced ignition mechanism of roof sandstone under uniaxial compression were explored, and the real ignition source of the gas explosion accident in Babao Coal Mine was revealed. The experimental results reveal that the intensity of PSCs of sandstone is higher than that of marble in the loading stage because the piezoelectric effect of quartz in sandstone enhances its mechanical-electrical sensitivity and leads to an increase in the discharge intensity. During the whole loading stage, the PSCs signals generated by sandstone are mainly attributable to the piezoelectric effect of quartz, while the PSCs of marble are mainly caused by the sliding friction between mineral particles. When the samples are in the compaction and elastic stages, PSCs are proportional to strain rate and stress rate respectively; when the samples enter the stage of plastic deformation and failure, the peak values of PSCs are positively correlated with the uniaxial compressive strength. Sparks can be seen in sandstone during the failure stage, which mainly results from electron avalanche caused by the damage of quartz grains under loading. The ignition source of the gas explosion accident in Babao Coal Mine is more likely to be sparks generated by the combined discharge of the extrusion friction and piezoelectric effect of roof sandstone, rather than coal spontaneous combustion.