An oscillation wave test system (OWTS) can carry high capacity load, and was generally used in long cables test. To improve the sensitivity of OWTS measurement system effectively, the limitations of typical impulse current detection method when used in long cables is analyzed theoretically, and an improved electromagnetic coupling method is present for OWTS. To compare the measure precision of two methods, different quantity of electric charge is applied in measure circuit. To analyze the characteristic of measurement signal in two method, partial discharge based on oscillating wave voltage is measured by using two methods. From the result, the improved electromagnetic coupling method has higher sensitivity, and more difficult to be interference by low frequency signal.