A severe rainstorm was observed in northern Xinjiang and east of southern Xinjiang from 15th to 17th of April 2005. The storm was triggered by a short wave which was separated from Middle Asian vortex with cold air supplemented from North. The result showed that heavy precipitation appeared in the area of minimum value of TBB less than -42℃. The maximum precipitation intensity was greater than 7mm h-1 while TBB was lower than -52℃. The precipitation intensity began to increase after strong reflectivity echo exceeded 20 dBz in 30 minutes from wind profiler in Urumqi. Water vapor was transported to rain belt mainly from 700 hPa to 850 hPa in 6 to 12 hours before rainstorm happened. The maximum water vapor flux was 12 g·(cm·hPa·s)-1. The 5-minute precipitation intensity was affected primarily by low-level jet in the previous stage of rainstorm. However, in later period of the low-level jet, water vapor, which was brought from large wind belt and the convergence intensity in middle level, played an important role. Finally, in the article we analyzed and discussed the forecast of the heavy rain evet in numerical prediction model of the Institute of Desert Meteorology in CMA, ECWMF and T639.