In this study, the characteristic and formation mechanism of convective cluster over Sichuan Basin on 6 May 2016 are analyzed with FY2 satellite data, NCEP reanalysis data and conventional data. The results indicate that the convective clusters tend to form at the buffer zone of the western Sichuan Plateau, with their cloud top brightness temperature less than -45℃ and maximum temperature gradient greater than 15℃. Meanwhile, the difference between the cloud top brightness temperature measurements from IR3 and IR1 can range from -5℃ to 0℃ and the difference of those from IR2IR1 is between 0℃ and 2℃. Heavy rain occurs in a few hours after the cloud top temperature quickly drops to the lowest temperature, the difference between the cloud top temperature measurements from IR3 and IR1 is near 0℃, and the difference of IR2IR1 is positive and the temperature gradient of 0℃. Furthermore, the heavy rain starts at the time when the brightness temperature starts to rise again. Typically, wide range of heavy rain is mainly produced by the severe convective clusters whose cloud top brightness temperature is less than -70℃ and it tends to happen within the lower and smooth regions with the cloud top temperature between -65℃ and -60℃ and the IR3 brightness temperature from -65℃ to -60℃. Moreover, it is not in conformity with the lowest temperature center of cloud top. Mechanism analysis shows that the clusters’ ambient characteristics include high instable convective energy, sufficient moisture and east wind flow. The cold airflow in boundary layer and convergence line on surface are the main mechanism of the convective cluster trigger. The enhancement of the vertical wind shear, and the development of the middle level warm airflow and the high level cold airflow jointly prompt the intensification of the severe convective clusters.