Railway oil tank truck oil unloading device and method

The invention provides an oil unloading device and method for a railway oil tank truck. The oil unloading device for the railway oil tank truck comprises an oil unloading crane pipe, the oil tank truck, an oil unloading pipe, a self-priming pump, a buffer tank and a vacuum pump assembly. The first input end of the oil unloading crane pipe extends into the oil tank truck; the first output end of the oil unloading crane pipe is connected with the oil unloading pipe through a first valve, and the end, away from the oil unloading crane pipe, of the oil unloading pipe is connected with the self-priming pump. A second output end of the oil unloading arm is connected with the bottom of the buffer tank through a second valve; the top of the buffer tank is connected with the vacuum pump assembly; and the second valve is opened, and the vacuum degree in the buffer tank is controlled through the vacuum pump assembly, so that part of liquid oil in the oil tank truck enters the buffer tank, and a first liquid level is for