To solve the thermal environment problem of high ground temperature tunnel construction and master the energy balance control method of the heat source and cold source in the tunnel, fresh air volume calculation formulas under water exposure with and without high temperature are deduced based on the principle of heat transfer and the law of energy conservation. The formulas are applied to  Gaoligongshan tunnel of Darui Railway, and the results show follows. (1) The theoretical formulas obtained are reliable, and the calculation error can be controlled within 6%. (2) The increase in ventilation can reduce relative humidity in the tunnel  obviously. (3) The fresh air with low temperature and humidity can effectively improve the environmental quality in the tunnel, but it is not universal in every condition, the heat environmental control method should be selected according to actual conditions.