Abstract: The paper aims to improve the forecast ability of extreme rainstorm in arid desert area and alleviate the local water resource shortage. The authors used the maps of conventional meteorological observation, precipitation of regional automatic weather stations, FY-2D satellite cloud pictures, meteorological elements of single station and NCEP reanalysis data to analyze the cause of a local extreme rainstorm happened on 15 May 2013 in Minqin of the arid desert area. The results showed that: this local rainstorm happened in the arid desert area which had very little precipitation, the rainstorm had the characteristics of special time, large rainfall intensity and long brewing time. The 500 hPa Xinjiang trough leading the cold air southward, low-shear line moving slow eastward, and ground wind field convergence were the major system which affected the extreme rainstorm. The water vapor gathered in southwest and southeast direction, the southeast jet was the main source. Low-level convergence, high-level divergence and the whole layer ascending motion were the dynamic conditions; the high value areas of K index, CAPE index and Si index, the high energy tongue areas of θse stretching position north by east were coincided with the rainstorm area; the combination and development of two convective cloud clusters was the important cause of the rainstorm.