The average depth of Baihetan Hydropower Station right bank tail water tunnel is more than 400 m; therefore, layer Ⅰexcavation adopts blind heading method, no wind shaft and tunnel, and ventilation lines are combined with construction branches，and can't set jet fans. The maximum one-stop adjective ventilation length is 3700 m, so the construction ventilation is very difficult. In order to ensure the ventilation effect, we calculated the air volume of each construction process. Using Fluent fluid numerical software, we established deep burying blind heading three dimensional and unsteady turbulent caverns model to study the blasting flow pattern and pollutants dispersion, distribution law, and verified using in-situ pollutant concentration field test. The results showed that tail water tunnel flow field is basically stable after 2 min ventilation. After excavation face blasting, pollutant concentration increases sharply, then decreases. After ventilation 12 min, pollutant concentration near tunnel face 3 m met standard requirement. After 15 min, pollutant concentration in all part was close to the standard allow scope. Air flow was smooth and ventilation effect was good.