Abstract: Operation of urban traffic is seriously affected by the rainstorm weather, and water is gathered on the surface and drivers' vision are obstructed, which leads to a decrease of road capacity. Based on the weather data and coil detector data in Shenzhen, the urban traffic flow characteristics under rainstorm, light rain, moderate rain and normal weather conditions were compared in this study, and their flow-density relationships were analyzed according to the Green-shields model. Moreover, the road capacity reduction coefficients for urban arterial and sub arterial roads were quantitative calculated, respectively. The results provide theoretical support for the emergency management of urban traffic operation under rainstorm weather.