Accurate interpretation of field electromagnetic sounding signals requires laboratory conductivity measurements of rocks under simulated physicochemical conditions at specific underground depths. Current laboratory measurements of conductivity corresponding to geophysical exploration depth of resource and energy still face challenges, including the lack of a proper high-temperature and high pressure simulation platform, or an accurate in situ electrical conductivity measurement circuit adaptable to the former. In this work, we developed a new system, including an autoclave device capable of simulating temperatures up to 350°C and pressures up to 350 MPa, simultaneously (approximately 13 km depth), and an accurate electrical conductivity measurement circuit embedded in the autoclave device. Feasibility tests were performed on saturated sandstones. The observed temperature dependence of electrical conductivity and the formation factor of our samples were consistent with previous studies, demonstrating the effectiveness of our system and it can be widely used in future geophysical exploration of shallow crust.