The invention provides a mixed refrigerant-expansive refrigeration-circulated natural gas liquefying method. The method comprises the following content that (1) four cold boxes, an expansive refrigeration circulating pipeline, a mixed refrigerant circulating pipeline and a natural gas pipeline are arranged; (2) the refrigerant of the expansive refrigeration circulating pipeline enters the box to be pre-cooled and enters an expansion machine after being subjected to three-stage compression and water-cooling, and the expanded refrigerant enters the cold box to provide the refrigeration capacity; (3) the refrigerant of the mixed refrigerant circulating pipeline enters the cold box to be pre-cooled and enters a throttling valve after being subjected to two-stage compression and water-cooling, and the throttled refrigerant enters the cold box to provide the refrigeration capacity; (4) natural gas of the natural gas pipeline sequentially is cooled by the four cold boxes in sequence and passes through the throttling valve, and the throttled natural gas enters a flashing evaporator and is separated by the flashing evaporator. The mixed refrigerant-expansive refrigeration-circulated natural gas liquefying method is used, the component of the refrigerant is reduced, the change sensibility of the component content in the raw material gas is lowered, the configuration and the storing are convenient, and the adaptability of an offshore floating environment is effectively improved.