Abstract: Based on the data of conventional meteorological observations, Guangdong regional automatic weather stations and Guangzhou Doppler radar, the weather process of westerly supercell tornado occurred in Gaoming District of Foshan City on 31 May 2020 was analyzed. The results show that the high-level divergence field which overlaps with the weak convergence area in the middle and low-level, and the deep and strong southwest warm and humid air flow in the middle and low-level, combined with the long-term maintenance of the surface convergence line, provide favorable weather background for the occurrence and development of supercell storm. Large Cape, strong low-level vertical wind shear and low LCL provide favorable environmental conditions for tornado occurrence. Tornado is produced in meso-β scale supercell storms, and radar detects obvious hook echo, echo suspension and low-level moderate intensity mesocyclone, but the mesocyclone scale is large and the diameter of mesocyclone is more than 6 km before and after the tornado hits the ground, and the tornado appears at the top of hook echo and the center of mesocyclone.