The invention discloses a high-low pressure conversion hot oil supply device. The high-low pressure conversion hot oil supply device comprises a stirring tank, a hot oil pump, a hot oil valve, a tee joint, an ultrahigh pressure stop valve, a pressure sensor, a stone, an exhaust valve, a pressure medium exchange disc, a cold oil valve and a cold oil pump. The stirring tank is connected with the hot oil pump through an oil pipe. An oil outlet of the hot oil pump is provided with the hot oil valve. The hot oil valve, the ultrahigh pressure stop valve and the cold oil valve are connected with the tee joint through oil pipes. The cold oil valve is arranged at an oil outlet of the cold oil pump. The ultrahigh pressure stop valve, the pressure sensor, the exhaust valve and the pressure medium exchange disc are connected with the stone through ultrahigh pressure oil pipes. The ultrahigh pressure stop valve is arranged in the high-low pressure conversion hot oil supply device, and after extrusion barrel filling, a high pressure area and a low pressure area are isolated. The ultrahigh pressure stop valve is simple in structure, and operation and maintenance are simple and convenient. The partition limiting pressure is large, and the application range is wide. During opening and closing, the torque is small, and labor is saved. A sealing structure is reasonable in design, and zero leakage can be guaranteed; and a sealing face is not prone to abrasion or scratching, the work life is long, and reliability is high.