The Rainfall is one of important factors affecting traffic safety on urban roads. The road traffic problems caused by rainfall result in great economic losses every year. The mech- anism of influence in macroscopic and microcosmic perspective was analyzed. The relations a- mong the factors influencing road traffic safety in macroscopic perspective were inspected. The issues of visibility, friction characteristics of road surface,traffic signs and markings and traffic psychology were discussed. The countermeasures for improving urban roads safety on the rain time were put forward.