The invention provides a differential pressure adjusting valve testing device and testing method. The method comprises the following steps: firstly, sealing an oil transportation channel inside a differential pressure adjusting valve, opening an oil inlet switch valve and an oil inlet adjusting valve, adjusting an oil inlet oil supply pump to enable reading of an oil inlet flowmeter to reach a required flow of a leakage test, adjusting an oil inlet adjusting valve to enable reading of an oil inlet pressure gauge to reach a required flow of the leakage test, observing whether flow reading is available on an overflow meter or not, if not, representing that the sealing property reaches the standard; and readjusting the oil inlet oil supply pump to enable the reading of the oil inlet flowmeter to reach a required flow of a pressure resistance test, readjusting the oil inlet adjusting valve to enable the reading of the oil inlet pressure gauge to reach a required flow of the pressure resistance test, opening an oil control switch valve, adjusting an oil control oil supply pump and an oil control adjusting valve to increase the reading of the oil control pressure gauge from zero, and when an oil fluid of an overflow tube flows out, observing whether the reading of the oil control pressure is greater than or equal to a given pressure resisting value or not, if so, representing that the pressure resistance reaches the standard.