In order to solve the problem that the cooling source of conventional gas hydrate hole-bottom freezing sampler is difficult to be stored for a long time and the core freezing efficiency is low, an external cooling source freezing sampling method is proposed. The cooling source is stored in the fishing device, which reduces the storage time in the hole and improves the storage efficiency. During the freezing process, nitrogen is injected into the freezing chamber to enhance the convection of heat transfer between cooling alcohol and core and to improve the core freezing efficiency. Low temperature alcohol（-130℃）, a mixture of liquid nitrogen and alcohol，is used as a cooling source. Cooling source storage test and core frozen experiment are carried out in this paper. During the procedure storing 30-minute cooling source, the frozen energy storage rate is 73.1%. The thermal efficiency between cold source and core is improved because the nitrogen is injected in the cooling source, the average temperature of the core drops to 14.9i2℃, the freezing efficiency is increased by 24.3% compared with the traditional way.The problem that the cooling source cannot be stored in the drill pipe for a long time can be solved by adopting the cooling source external sampler structure. The problem of low core freezing efficiency can be solved by passing nitrogen into the cooling source to increase the convection of heat transfer. This paper provides a feasible method for Natural gas hydrate sampling.