Gas water heater and intelligent water drainage anti-freezing method

The invention discloses a gas water heater. The gas water heater comprises a controller, a heat exchanger, a first water inlet pipe, a second water inlet pipe, a first water outlet pipe, a second water outlet pipe, a shower head, a water flow sensor, a temperature sensor, a water drainage pipe and a four-way reversing valve. A water inlet of the first water inlet pipe is connected with an external water supply pipe, a water outlet of the second water inlet pipe is connected with a water inlet of the heat exchanger, a water inlet of the first water outlet pipe is connected with a water outlet of the heat exchanger, and a water outlet of the second water outlet pipe is connected with the shower head. A water outlet of the first water inlet pipe, a water inlet of the second water inlet pipe, a water outlet of the first water outlet pipe and a water inlet of the second water outlet pipe are sequentially connected to four channel ports of the four-way reversing valve. The water flow sensor is arranged on the first water inlet pipe, the water drainage pipe is connected to the second water outlet pipe, the temperature sensor is arranged on the second water inlet pipe, the controller is connected with the temperature sensor, the water flow sensor, the four-way reversing valve and a stop valve through signals. The invention further discloses an intelligent water drainage anti-freezing method.