The design of the operation ventilation of a highway tunnel in Kunming is studied in the paper. Ventilation solutions with/without natural ventilation intakes are presented, and in the end, natural ventilation solution is adopted for the tunnel. The operation ventilation of the tunnel with natural ventilation intakes, as well as the diffusing range of the pollutants at the tunnel portal are studied by means of SES4.1 and CFD simulation software, and the environment is evaluated. The results show that the emissi on and diffusing of pollutants at the tunnel portals can be brought under effective control if natural ventilation intakes are installed on the top of the tunnel and decentralized emission mode is adopted.