Abstract ： Research purposes ： The air volume and time needed for discharge of smog induced by tunnel drilling and blasting construction are the keys to tunnel construction ventilation design. The popular air volume calculation formula for discharge of smog is mainly based upon MAC standard，and there is no case about PC - STEL standard. As a result， analysis and study are made on air volume calculation using PC - STEL standard. Research conclusions ：( 1) The air volume calculation formula based on PC - STEL standard is diferent from that based on MAC standard，and the calculation result based on PC - STEL standard is smaller tlian that based on MAC standard under same conditions，and is beneficial to energy conservation. (2) The air volume calculation formulas for different ventilation modes(i. e. air - supply mode，air - discharge mode and mixing mode)，are different when using PC - STEL standard. (3) The research results can provide reference for tunnel construction ventilation and design，to promote the application of national standards.