The utility model provides a device for detecting large -scale transformer bushing end seal leaks a little, including air chamber, a valve, B valve, vacuum pump, its characterized in that the lower extreme of air chamber is equipped with the B ring flange, even there is the A pipeline on the lateral wall of air chamber, be equipped with the B valve on the A pipeline, the one end of A pipeline is still welded set A ring flange of bag pipe with flange joint's mode and a centre and is linked to each other, the upper end of air chamber is equipped with the A valve, the upper end of A valve is equipped with the B pipeline, one side of air chamber still is equipped with high pressure air compressor and vacuum pump, even there is the helium mass spectrograph in the discharge port department of vacuum pump, the technological problem who in the past detected the slight leakage of large -scale transformer oil charge operation sleeve pipe end seal can be solved, the electric power system security performance has been improved.