Abstract: In order to optimize airflow parameters and zeroposition control system of the closed steam hood in paper machine’s dryer section, the air condition both inside and outside of the hood was firstly analyzed. The pressuredifference changing curve between inside and outside of the hood was established under mechanical ventilation. On the other hand, the influence of air temperature or volumedifference between supplied and drawn air on zeroposition was also quantitatively analyzed. Finally, the quantificational zeroposition control model was established. The results indicated that the air temperature inside upper hood, the variation of which is about 55 % of the variation of supplied air temperature, is directly propotional to the level of zeroposition. The variation of supplied air moisture can cause the volumedifference between supplied and drawn air changing by about 12.5 % which has an inverse propotion to the level of zeroposition. According to the principle of adjusting the volumedifference between supplied and drawn air, the deviation of zeroposition can be quickly regulated by setting feedforward control system.