• New variables for evaluating the smoke blocking efficiency and water curtain momentum ratio are introduced. • The effect of water spray intensity and momentum ratio(R) on smoke blocking efficiency are analyzed. • The reasonable conditions for safe evacuation of the trapped people are analyzed. With an appropriate air supply, smoke can be controled by water curtain system effectively in an urban underground road. In this study, smoke blocking efficiency and water curtain momentum ratio are newly introduced. These parameters are used to quantitatively characterize the effects of smoke control and thermal insulation. Numerical simulation method is used in this paper. The results indicate the following: the smoke efficiency decreases as water spray intensity increases, and when the water spray intensity is 0.5L/(m·s), increasing the water spray intensity by 0.5L/(m·s) may be beneficial to increase the smoke blocking performance. The smoke blocking efficiency and the thermal insulation efficiency decrease first and then increase along with the increase in the momentum ratio R. Better smoke blocking and heat insulation performance occured when R ≤ 2. In this condition, the visibility at the 2 m above the floor is above 10 m,and the temperature is lower than 60 °C. It can ensure the safe evacuation of the trapped people.