The invention relates to the civil engineering field and specifically relates to a basement foundation plane leak detection method and system with house subsoil. The method comprises the following steps: on a basement foundation plane, taking a suspected leakage area as a detection area, and after cutting the detection area, observing water seepage flow direction; in the detection area after excavation, arranging a layout interval; summarizing water seepage parameters corresponding to the layout interval; according to the water seepage parameters, obtaining function relationship between waterseepage attenuation and layout interval; and according to the function relationship, calculating position relationship between a water seepage source and the detection area. The method can solve the problems that when water leakage occurs in a basement foundation raft plate, processing is complex and efficiency is low in the prior art; and the method is simple to operate, and does not need large-area excavation, thereby saving labor and cost.