In the line of paper PMs, the paper moisture is an important indicator of the paper quality and the control of the paper moisture is undertaken by the drying system. The control of the drying section air to ensure moisture has three tasks: air heating and blowing control, dew point temperature control and input-output air balance control. Dew point temperature in the drying section is the important physical quantity which has a great effect on the evaporation rate of drying paper. Dew point temperature of the air in the drying section is determined by two quantities:the relative humidity (%RH) and the average temperature of the air in the drying section. This paper analyzes and discusses the dynamics of dew point temperature and investigates the effect of elements on dew point temperature in order to design the control system of dew point temperature.