With experiment test, a second-order orthogonal experiment was carried out to analyze the weight of factors affecting H₂S and NH₃ concentration in sludge dewatering of underground wastewater treatment plants:temperature, humidity and exhaust volume, and according to pollution level and energy consumption, a comprehensive evaluation index was put forward. The results indicate that Interaction between temperature and exhaust volume is important to H₂S and NH₃ concentration (p<0.05). When the outdoor temperature is 20℃, the H₂S and NH₃ concentration of the dewatering machine room is the lowest. It is reduced by 2.5 times compared with 35℃. According to the comprehensive evaluation index, the minimum K value is 4.5 in the ventilation frequency of 2.7. Below 2.7 times of ventilation, the odor concentration is too high, and the energy consumption is too large when higher than the 2.7 times of ventilation. Therefore, the most appropriate number of ventilation is 2.7 for dewatering room with treatment capacity ten thousand per day.