The invention discloses a high-pressure hydraulic pump testing pressure stabilizing system and method. The pressure stabilizing system comprises a tested hydraulic pump, a high-pressure energy accumulator, a low-pressure energy accumulator, an energy accumulator switching device, a pressure sensor and a control part. The high-pressure energy accumulator is connected with a hydraulic pump outlet oil path. The low-pressure energy accumulator is connected with the hydraulic pump outlet oil path through the energy accumulator switching device. After the tested hydraulic pump is started, the pressure sensor monitors the oil path pressure, and when the pressure is smaller than the preset value, oil enters the low-pressure energy accumulator through the energy accumulator switching device, and system pressure stability is maintained through the low-pressure energy accumulator. When the pressure is larger than the preset value, the control part controls the energy accumulator switching deviceto conduct switchover, the oil path and a low-pressure energy accumulator channel are cut off, and system pressure stability is maintained through the high-pressure energy accumulator.