Abstract: Using conventional meteorological observations data, the circulation background field of the westerly tornado in Jiulong Town, Huangpu District, Guangzhou City at 17:40, May 21, 2014 is analyzed. FNL and ERA5 reanalysis data are used as the background field to simulate the tornado process, and the influence of different reanalysis fields on the simulation results are studied.The results show that from the analysis of radar echoes, vertical velocity, horizontal wind field and hydromorphic material, the simulation of the westerly tornado with FNL data as the initial field is better than that with ERA5 data as the initial field. The FNL reanalysis data as the initial field and boundary field can effectively simulate the super monolithic structure of the westerly tornado. At 17: 45 on May 21, 2014, the convective storm was similar to the classical super monolithic structure, with hook-like echo features and inlet gaps, and its vertical structure showed that the strong echo tilted to the east to form a dome structure. At 17: 50, there was a strong updraft and a back-side downdraft at the hook echo of the super monomer, which had the necessary conditions to generate a tornado; the vortex features were obvious from the low-level plane of vertical vorticity, which extended from 250m to 2 km in height. Tornadoes may occur in small-scale cyclones ,which is streching northwestward from the ground to 2 km.