The invention provides an oil injection tool, which aims to solve the problem of long oil injection time for a distribution transformer in overhauling and rush repair of the public distribution transformer. The oil injection tool comprises a funnel and a buoy; the funnel comprises a funnel body and an oil drain pipe arranged below the funnel body; the buoy comprises a floating ring, an inner pipe and an outer pipe, and an oil storage trough is formed between the inner pipe and the outer pipe; and the outer pipe is sleeved on the oil drain pipe, the oil drain pipe is sleeved on the inner pipe, an oil drain clearance is reserved between the oil drain pipe and the inner pipe, a convex eaves surrounds the outer wall of the upper end of the inner pipe, and the convex eaves is lapped onto the funnel body. The oil injection tool is provided with the funnel and the buoy, oil flows through the funnel and the inner pipe of the buoy and enters an oil tank, the buoy is jacked by the oil when the oil in the oil tank arrives at a specified position, the convex eaves of the buoy is separated from the funnel body of the funnel, oil supply is stopped after a worker observes the situation, and excessive oil enters the oil storage trough along the funnel body in the process, so that the adding quantity of oil in the oil tank is accurately controlled, the working efficiency is high, and the spent time is short.