The invention relates to a method and device for controlling a gas water heater with the cool bathing mode. By adoption of the automatic constant-temperature-type gas water heater, the function of providing hot water at any temperature can be achieved, and the 'cool bathing mode' is added. The water outlet temperature is gradually changed along with the duration of bathing. After the water outlettemperature reaches a certain temperature, the temperature is kept for a period of time at first; and then the water temperature begins to drop, after the temperature is decreased to a certain temperature, the water temperature is kept unchanged all the time, and the difference value of the two temperatures is at most 3 DEG C. After the 'cool bathing mode' function is used by users in summer, thehot water temperature at the later period of bathing can be lowered gradually, the temperature of the inside of a shower room can be lowered accordingly, the condition that people can perspire at onceafter taking a bath can be eliminated completely, and meanwhile human bodies can feel fresh, cool and comfortable. In addition, the users can set the water outlet temperature and time, and bathing can be made more enjoyable according to bathing habits of the users.