A water temperature control system and a water temperature control method are provided. The water temperature control system includes a thermostatic spool, a temperature sensor, a controller, and a stepper motor. The thermostatic spool is configured to mix water at a first temperature and water at a second temperature to produce output water. The temperature sensor is configured to sense a current water temperature of the output water based on a sensing frequency to provide a current water temperature signal. The controller is configured to provide a step number control signal according to a target water temperature signal and a current water temperature signal. Based on a step frequency greater than the sensing frequency, the stepper motor is configured to provide a step number according to a step number control signal to adjust a flow rate of the water at the first temperature and a flow rate of the water at the second temperature.