In order to accurately predict the dynamic variation of water temperature of river-canal,a rapid dynamic water temperature calculation method that can respond to the real-time meteorological variation is put forward herein through generalizing the dynamic process of the water surface heat exchange and calculating all the surface heat fluxes in items; in which the dynamic meteorological process and the water temperature variation caused by it are taken into account,and then the lag of the response from the mean cross-sectional water temperature to the meteorological variation is considered in the calculation through the introduction of the concept of equilibrium lag time. With the actual case of the water intake open channel for a power plant in Hainan Province,it is indicated that the real-time response of water temperature to the meteorological condition can be correctly captured with this method,thus the dynamic process of the water temperature along river-canal can be accurately and efficiently simulated as well. The introduction of the concept of equilibrium lag time makes the simulation error decreased by 39%,while the water temperature on river-canal calculated by the model is more sensitive to wind speed,air temperature and cloud cover. Under the background of the global climate change and frequent occurrence of regional extreme weather,this study can provide a rapid and effective method for assessing river water temperature status and estimating the water temperature rise of open channel.