Abstract Numerical simulations are carried out to study the water curtain systems for fire evacuation in a long and narrow water tunnel under construction by shield tunnelling machine (STM). The designed fire is located near the working face with a heat release rate of 40 MW. In numerical simulations, the grid resolution is analyzed. The temperature, soot density, species concentration and visibility at different cross sections with different water curtain conditions are studied. The water curtain can partially prevent the smoke from spreading outside, and cool the smoke outside evidently for a better evacuation. It can appreciably decrease the carbon dioxide concentration and increase the oxygen concentration outside the water curtain. However, the water curtain will largely increase the soot density and decrease the visibility at the lower part of the water tunnel. The droplet from the water curtain will put impact on the flow and make a turbulent flow nearby.