The invention discloses a method for preventing a waste heat recovery device from flue gas dew point corrosion, which aims to solve the problem that the prior method has a danger of making the waste heat recovery device produce the flue gas dew point corrosion. The method comprises the following steps: A, an acid dew point measurement instrument (1) is used to measure a flue gas acid dew point temperature Tm at a flue gas outlet of the waste heat recovery device and transmits the Tm to a comparator (3), and a wall surface temperature transmitter (2) is used to measure a flue gas side wall surface temperature Tgm of a heat transfer element close to the flue gas outlet, and also transmits the Tgm to the comparator; B, the comparator adds the Tm by minimum excess temperature difference dTmin(5-10 DEG C), compares the sum of the Tm and the minimum excess temperature difference dTmin (5-10 DEG C) with the Tgm to obtain regulation temperature difference delta Tgm, and transmits the delta Tgm to a temperature regulator (4); and C, the temperature regulator produces and outputs a heat exchange amount adjustment signal, controls a heat exchange amount adjustment device to actuate, and regulates the heat exchange amount of the waste heat recovery device to ensure that the Tgm is 5 to 10 DEG C higher than the Tm, therefore, the flue gas dew point corrosion is avoided.