Measured results show that tunnel wall temperatures are lower than airflow temperature in some places of high temperature mines. This paper firstly set up the temperature distribution mathematical model inside the surrounding rocks by analysis of heat and moisture transfer between tunnel rock surface and airflow, and secondly deduces a formula that calculates tunnel wall temperature with function of water evaporation heat transfer considering airflow velocity, temperature and humidity, and thirdly quadratic curve is obtained by making mathematical transformation to this formula. Theoretical and graphical method reveal the critical condition of wet wall temperature which is lower than air temperature, the phenomenon that the tunnel wall local temperature covered with water is lower than airflow temperature is explained theoretically.