The invention discloses a capacitor seal strength detection device and a detection method thereof. The detection device comprises a test piece clamping and sealing mechanism, a hydraulic system, and a pressure detection storage system; wherein the test piece clamping and sealing mechanism comprises a guide shaft, a linear bearing, a frame, a chuck installation plate, a nut, a screw rod, a hand wheel, a snap ring, a three-claw chuck assembly, a jack catch, an oil way connection disc, a rubber sheet, a filling member, and an expansion stopping ring. The hydraulic system comprises a hydraulic pump station, an overflow valve, a pressure reducing valve, a first electromagnetic valve, a throttle valve, a pressure meter, and a second electromagnetic valve. The pressure detection storage system comprises a recorder and a pressure transmitter. The provided detection device uses oil pressure to detect the capacitor seal strength, the pressure adjustment is convenient, the detection results are accurate, and the dynamic data during the detection process can be completely stored for following analysis.