A cooling system includes a cooling device, a controller and a defrosting unit. The cooling device has a compressor, a condenser, an expander, an evaporator, a cooling channel and a coolant. The coolant is functioned in the evaporator to thermally exchange with a working fluid in a pipe. The controller is adapted for controlling the temperature of the working fluid by controlling the cooling device. The defrosting unit has a switch disposed on the cooling channel and located between the compressor and the condenser, and a defrosting channel connected with the switch. After passing through the switch, the coolant is optionally fed to anyone of the cooling channel and the defrosting channel. After flowing through the defrosting channel, the coolant passes through the evaporator and then flows back to the compressor. As a result, the cooling system is capable of fast defrosting without using a heater.