As an important part of hydropower station, the thermal and humid environment of tailwater surge chamber affects the safe and stable operation of hydropower station. In the actual project, it is found that the fog and condensation in the tail control room are serious, and the operation of internal equipment and the health of staff are affected. According to the actual situation of the tailwater surge chamber of XLD hydropower Station, three humidity control schemes: mechanical ventilation, cooling dehumidification and cooling dehumidification and mechanical ventilation are proposed, and compares the control effects of the three schemes under the most unfavorable conditions in summer through numerical simulation, so as to find the optimal scheme for the humidity control of the tailwater surge chamber. The simulation results show that the mechanical ventilation scheme can not effectively solve the problem of high humidity in the tail chamber, and the air at the end and bottom of the chamber is saturated in many places. The cooling dehumidification scheme can play a certain dehumidification effect, but the air flow distribution is not uniform, the relative humidity of the middle and end still does not meet the requirements. The cooling dehumidification and mechanical ventilation scheme can reduce the humidity of the tail adjustment room working area to less than 80%, and ensure that the indoor air temperature and humidity distribution is more uniform.