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利用高分辨率的模式输出资料，对2008年6月广西致洪暴雨及其中尺度低涡（简称广西涡）进行了等熵位涡（IPV和湿位涡（MPV）的诊断分析。结果表明，低值等熵面上正IPV带的位置和强度可以反映暴雨的落区和强度，等熵面上的西风气流可分别将高纬度干冷和低纬度暖湿的高值IPV向广西涡处输送，使得广西涡维持高IPV。高值等熵面上南部的IPV存在下传现象，有利于其下游的广西涡IPV的增长，从而使得广西涡强烈发展、降水增强。利用MPV守恒原理的分析表明，持续性暴雨出现在高值等熵湿位涡前方的对流不稳定区中；暴雨区南北两侧对流层中高层的冷空气下沉时对流稳定性减小，对应的气旋性涡度增大；而暖湿气流沿着干冷空气爬升，它与具有强涡度的沿等熵面下滑的干冷空气发生强烈的辐合，使得涡度急剧增强，再加上地形的强迫抬升作用，形成强烈的垂直上升运动，导致涡旋强烈发展。等压面上的MPV及其分量分布显示，对流层中低层MPV负值带对雨带有指示作用，强降水时段对应着对流不稳定和条件性对称不稳定。“,”The potential vorticity （PV） on isentropic surface and moist potential vorticity （MPV） di- agnoses in the mid-June of 2008 during Guangxi flashflood rainstorm process under the influence of me- soscale vortex （Guangxi vortex for short） are carried out using the high-resolution model data. The results show that the location and strength of positive PV on low-value isentropic surface reflect the area and in- tensity of heavy rain dry and cold high-value isentropic potential vorticity （IPV） on high-latitude and warm and moist high-value IPV on low-latitude are, respectively transported to vortex area in Guangxi by westerlies on isentropic surface, resulting in the maintenance of high-value IPV in Guangxi vortex. While on the high-value isentropic surface, there is transportation of southern IPV to its downstream, which is beneficial to the IPV growth of Guangxi vortex which is in its downstream, resulting in strong develop- ment of Guangxi vortex and precipitation enhancement. The analysis on the MPV conservation principle shows that continuous heavy precipitation appeared in the convectively unstable area in front of high-value isentropic moist potential vorticity. The convective stability decreases with the going down of cold air in mid- and upper-level troposphere on north and south sides of rain area, making the corresponding cyclonic vorticity inerease~ while the warm and moist air climbs along dry and cold air, and there is strong convergence between the warm air and the cold one gliding down the isentropic surface, making the vortic- ity sharply increase, and with the uplifting effect forced by terrain, strong vertical ascending motion is formed and the vortex strongly develops. The distributions of isobaric surface MPV and its components show that negative MPV in the lower-level troposphere can denote the heavy precipitation, and there is convective instability and conditional symmetric instability during heavy precipitation period.