The invention provides a teaching device used to simulate an oil immersed transformer. The teaching device comprises a cabinet body (8), in which is disposed an oil tank (9). A flat plate (1) is disposed on the top part of the cabinet body (8), and a submersible pump (10) is disposed in the oil tank (9). The teaching device also comprises a gas injection tube (2), a thermometer (3), a gas intake box (4), a gas relay (5), an oil barrel (6), and a respirator (7). The oil barrel (6) is provided with an oil scale and a pointer oil level indicator. According to the teaching device, the oil tank (9) is used to simulate a transformer body, and the oil barrel (6) is used to simulate an expansion tank. During use, the gas injection tube (2) is used to inject gas to simulate motion of light gas, and by controlling oil flowing speed, motion of heavy gas is simulated, and then a student can observe the working process of the gas relay (5), the respirator (7), and other objects, and therefore the abnormal phenomena of the transformer body can be known in a direct and three-dimensional way, and high learning efficiency can be acquired.