The temperature of flue gas should be controlled to be higher than the acid dew point to avoid fouling and corrosion of heating surfaces in the second pass of boilers. Decreasing the temperature of flue gas in boilers is one of the most effective ways to improve thermal efficiency, enhance electrostatic precipitator efficiency, and decrease water consumption of the desulfurization tower. Accurate knowledge in predicting acid dew point is required. Thus, based on previous research achievements, a measuring device is designed based on the principle of conductive dew point meter, and the acid dew points under different flue gas conditions are measured in this work. An improved thermodynamic correlation formula between the acid dew point and its influencing factors is also derived based on previous research achievements. Then, a semiempirical prediction model that considers the functions of H2SO4 and H2O is proposed. The proposed prediction model is validated by field test data, experimental data, and prediction models reported in previous studies.