The invention discloses a high-voltage instrument transformer, which comprises an outer insulating porcelain sleeve, an expander shell, a corrugated expander, a sealing plate, first insulating sealingsleeves, second insulating sealing sleeves, a primary winding, a primary wiring terminal, secondary windings, a detection box, a sealing cover, a fixing plate, secondary detection terminals, limitingblocks, springs, connecting flanges, sealing flanges, leakage-proof bases, upper covers, levers, floating blocks, ejecting blocks, micro switches, indicator lights and supporting feet. The primary winding is sealed through the first insulating sealing sleeves and the second insulating sealing sleeves, oil leakage can be prevented, insulating oil in the outer insulating porcelain sleeve can be prevented from leaking into the leakage-proof bases, and abnormality of the instrument transformer is prevented. After the sealing cover is dismounted, the two secondary detection ends pop out, and a user can conveniently carry out testing or wiring. The defect that the secondary wiring terminals of a traditional instrument transformer retract into the shell to cause difficulty in wiring is overcome.