During the rescue of Shijingshan tunnel flood accident, the working environment deteriorated due to the unreasonable ventilation system, and the rescue work could not be carried out normally. Therefore, the existing ventilation system is optimized in an emergency manner. Meanwhile, network calculation and continuous monitoring of ventilation effect are carried out for the ventilation system after emergency optimization. The results show that: (1) Among the fans available at the site, the 22 kW, 30 kW, and 37 kW jet fans installed in the transverse passage cannot meet the air volume demand of the left and right holes, and only the axial flow fans of 160 kW can meet the air volume demand of the left and right holes, and the wind speed in each section of the tunnel meets the minimum wind speed requirement. (2) After the emergency optimization of the ventilation system, the concentration of CO in the left and right holes is greatly reduced and keeps below the national standard concentration, the ventilation effect is significantly improved, and the operating environment is significantly improved.