The invention provides a method for controlling a three-valve heat exchanger by the temperature difference. A first valve, a second valve and a third valve are arranged at inlets of a first heat exchange pipe, a second heat exchange pipe and a third heat exchange pipe, a first temperature sensor, a second temperature sensor and a third temperature sensor are respectively arranged in a left side pipe, a center pipe and a right side pipe and are used for detecting the temperature in the left side pipe, the center pipe and the right side pipe, the first temperature sensor, the second temperatureand the third temperature sensor are in data connection with a controller, the controller extracts the temperature data of the left side pipe, the right side pipe and the center pipe according to thetime sequence, and obtains the temperature difference or the accumulation of the temperature difference change through the comparison of the temperature data of adjacent time periods, and when the temperature difference is lower than a threshold value, the controller controls the opening and closing of the first valve, the second valve and the third valve so as to control whether first fluid, third fluid and second fluid are subjected to heat exchange or not. According to the method, the new fluid is started to carry out alternate heat exchange by detecting the detection temperature differenceor the accumulated temperature difference change, so that the vibration of an elastic tube bundle is continuously driven, and the heat exchange efficiency and the descaling operation can be further realized.