Introduction  In order to analyze the flow field characteristics of the longitudinal jet ventilation system in the tunnel.

  Method  The CFD software was used to simulate the longitudinal jet ventilation system of highway tunnel with different number of jet fans， and the flow field characteristics were analyzed.

  Result  It can be seen that， due to the jet action of the jet fan， the jet airflow is attached to the top of the tunnel. And the distinct low-speed flow area is formed near the ground within 30 m after the jet fan. And at the same time， increasing jet fan can increase wind speed in the tunnel.

  Conclusion  It is suggested to set a small downward inclination angle at the outlet of the jet fan or to reduce the installation height of the jet fan appropriately in order to improve the flow field.