In order to explore the smoke and heat insulation performance of water curtain in unban road tunnel with lateral exhaust, and provide reference for water curtain design and fire evacuation, numerical simulation of water curtain model is conducted by FDS. Under the fire scale of 8 MW and considering the double/four nozzle layout on tunnel top, the influences of factors, i.e. the pressures of water sprayhead of 0.08 MPa, 0.1 MPa, 0.25 MPa and 0.4 MPa, the amount of smoke exhaust, distance between exhaust vents and number of exhaust vents, on smoke and heat insulation performance are studied; the variation laws of exhaust scope, temperature and visibility are analyzed and compared; and the evacuation environment of tunnel is evaluated. The results show that: (1) The water curtain system weakens the spread of smoke in the tunnel, prevents the tunnel temperature from rising too fast and improves the visibility of the tunnel. (2) The water curtain system is more effective in insulating smoke and heat as the amount of smoke exhaust increases, the distance between exhaust vents decreases and the number of exhaust vents increases. (3) However, the effect of water curtain on tunnel visibility improvement only keeps in the early and middle stages of the fire, and the effect will weaken in the later period. Therefore, it is necessary to carry out fire rescue work in the early and middle stages of the fire.