Abstract: By using the datum of general observations, numerical weather prediction products and satellite information in satellite images, it analyzes a heavy torrential rain which occurred in the southeast of Tibetan Plateau on May.15 to 16, 2007.The results show that:the direct effective system is the change from Tibetan high and subtropical high, the trigger is cold advection from high attitude, the stability of the subtropical high is the main reason to maintain the precipitation time, and, the storm of bay of Bengal played a key role for the vapor transportation.The result from forecast tests of the numerical products is:vertical velocity, divergence, water-vapor flux and the moisture flux divergence of T213 are significant for the real forecast.