Abstract: In order to solve the heat load problem caused by the power enhancement of air-cooled diesel engine, the temperature distribution characteristics of air-cooled diesel engine cylinder head and liner under the external characteristics were studied through the temperature test of cylinder head and liner. Results show that the temperature of the cylinder liner wall decreases gradually from top to bottom. The the temperature gradient of the the upper end point of the cylinder liner relatively higher, and the temperature gradually increases from the inside to the outside of the air pressure chamber. The temperature of the cylinder liner is lower near the inlet side and higher near the exhaust side, and increases with the increase of the rotational speed. The overall temperature distribution of the cylinder head fire surface is not uniform. The highest temperature is in the nose area of the cylinder head. The relatively lower temperature is near the intake channel side of the cylinder head, and the relatively higher temperature is near the exhaust channel side of the cylinder head. And the maximum temperature difference of cylinder head fire surface is more than 70 ℃. Under external characteristic conditions, the temperature of the fire surface of the cylinder head does not fluctuate significantly with the change of rotational speed since the fan flow and the thermal load of the cylinder head both increase with the increase of the rotational speed, thus cooling capacity is enhanced. At a constant speed and with different powers, the temperatures at measurement points of the cylinder head and liner increase linearly with the rise of power.