The invention provides a downhole oil-water interface detector which comprises a detection sensor D and a ground detector M. A plurality of detection structures are arranged on the detection sensor D, first ends of the multiple detection structures are electrically connected with one another, second ends of the multiple detection structures are connection contact points which are sequentially arranged along the height directions of the detection structures at intervals, and each detection structure comprises a detection resistor R; the ground detector M is connected with the detection sensor D, measurement voltages Vc can be outputted to the detection sensor D by the ground detector M, and measurement currents Ic which flow through the detection sensor D can be detected by the ground detector M, so that the heights of oil-water interfaces can be judged according to the measurement currents Ic. The downhole oil-water interface detector has the advantage that detection effects can be improved by the downhole oil-water interface detector.