The invention discloses a refrigerant filling method for a thermosyphon oil cooling refrigeration system. The thermosyphon oil cooling refrigeration system is filled with a refrigerant by adopting filling equipment mainly composed of a refrigerant container, a distribution station, a main pipeline and three distribution pipelines; a refrigerant inlet valve is arranged on the main pipeline, and thedistribution station is provided with a first refrigerant outlet valve, a second refrigerant outlet valve, a third refrigerant outlet valve and a pressure gauge; the first refrigerant outlet valve, the second refrigerant outlet valve and the third refrigerant outlet valve are sequentially connected to a pipeline between an evaporator and a low-pressure circulating liquid storage device, a pipeline between a condenser and a thermosyphon liquid storage device, and a pipeline between a high-pressure liquid storage device and a throttle valve through the three distribution pipelines correspondingly; and one end of the main pipeline is connected to the refrigerant container, and the other end of the main pipeline is connected with the distribution station. The refrigerant filling method has the advantages that the filling equipment which is simple in structure and convenient to operate is adopted, safety and reliability are achieved, the procedure is clear, and the filling efficiency is high.