To reveal the causes of the abnormal precipitation during the strongest plum rainy season in Guizhou since 2000, the Tianqing precipitation data was used to identify the years with the strongest plum rainy season in Guizhou since 2000 and their precipitation characteristics. Furthermore, the NCEP/NCAR reanalysis data and Fengyun FY-2G blackbody brightness temperature (TBB) data were utilized to diagnose and analyze the reasons for the abnormally high precipitation in Guizhou during the strongest plum rainy season and the causes of extreme precipitation. The conclusions are as follows:(1)In the plum rainy season of 2020, the cumulative precipitation in Guizhou was the second-highest since 1961 and the most anomalous year since 2000. The rainstorms were concentrated from early June to early July, with extreme precipitation intensities on June 23rd and 29th.(2)The frequent rainstorm processes and extreme rainstorms in Guizhou during the plum rainy season of 2020 were closely related to the general background of the Yangtze-Huaihe River Basin plum rains.(3)During the plum rainy season of 2020, mesoscale low-vortex systems that influenced Guizhou were frequent, and mesoscale convective systems were very active. Most of these mesoscale systems were initially formed in the western part of Guizhou, developed and strengthened within the province, and led to heavy rainfall weather. Mesoscale convective complexes (MCCs) were the direct influencing systems for the extreme precipitation on June 23rd and 29th.(4)In the plum rainy season of 2020, the low-level jet stream was abnormally active, especially in the early and late parts of late June and the late part of early July, with three sustained and intense low-level jet streams. This provided exceptionally abundant water vapor conditions for the persistent heavy rain processes, the three most widespread rainstorm processes, and extreme rainstorms during the plum rainy season. The research results aim to provide a basis for further improving the forecasting of persistent heavy rain, flood-inducing rainstorms, and extreme rainstorms during the plum rainy season.