Abstract: Adverse weather conditions such as rain,snow and fog have significant impacts on highway traffic operation and safety. This paper emphasized rain effects on characteristics of vehicle speed,based on the traffic and road weather data of detectors positioned on the segment between Jinshan and Wuhannan interchange of Jinggangao( G4) expressway in Hubei province. Focusing on the rain weather element,this paper analyzed the effects of rain on the mean speed and speed variation by rain or non-rain weather or under different rain intensities; speed characteristics were deeply explored considering different factors of traffic lane,vehicle types and time hour,utilizing detailed traffic data containing traffic lane and vehicle type information. The comprehensive speed prediction model under rain weather condition considering several factors was also built based on the classic traffic flow theory of V-K relation by Greenshield,and the goodness-of-fit of the speed prediction model reaches 80% approximately. The research results can be useful or as a reference to the analysis of rain on traffic safety and operation,traffic capacity analysis under or decision-making of traffic control measures such as variable speed limit under adverse road weather conditions.