An analysis of the climatic characteristics, circulation situation, impact system and mesoscale convective environmental conditions in 23 extreme rainstorm events in Sichuan Basin during 1981-2015 is performed by using conventional data and NCEP/NCAR reanalysis data. It is found that: (1) most extreme rainstorm events occur in continuous rainstorm processes, and rainstorms start ahead of the extreme storms, with rainstorm centers mainly in the northwest and southwest of Sichuan Basin. (2) The extreme rainstorm events occur mainly under the 500 hPa circulation background of “easthigh pressure and westlowpressure” and “shear between two highpressure”. Subtropical high would stretch toward northwest in 24 h during the rainstorm process in the “easthighpressure and westlowpressure” pattern. But subtropical high acts irregularly during the rainstorm process in the type of the “shear between two highpressure”. (3) Three extreme rainstorm events occur with landing typhoon, and the strong water vapor transportation formed by the outer circulation of typhoon has a direct impact on the heavy rain. Six extreme rainstorm events occur because of the blocking effect of the longdistance sea typhoon moving to west or north, and it is conducive to the maintenance of the heavy rain. (4) The main trigger system of the “easthighpressure and westlowpressure” is the southwest vortex and the plateau vortex while the main trigger system of the “shear between two highpressure” is the shear line, and the 700 hPa level has cold advection invasion. Two types of rainstorms occur on the divergence zone of the northeastern part of South Asia high pressure at 200 hPa, and the rainstorm center is located in the lowlevel high specific humidity area and convergence center. The stronger southerly airflow in the type of “easthigh pressure and westlowpressure” makes the rainstorm center located in the northwest of the basin, and the weaker southerly airflow in the type of “shear between two highpressure” causes the rainstorm center to stay in the southwest of the basin. (5) The characteristics of high specific humidity in the low level, high relative humidity in the whole layer, thick warm clouds, long and narrow CAPE, small vertical wind shear, high efficiency precipitation, and positive anomalies of 850 hPa humidity and pseudoequivalent temperature appear during the extreme rainstorm processes. And the 850 hPa pseudoequivalent potential temperature significantly decreases after the rainstorm. Based on the above, the conceptual model of extreme rainstorm in Sichuan Basin has been built, and it would benefit the operation of prediction.