Using the reanalysis data and WRFV3.6.1 model, the EF2-level tornado process which occurred in Sanshui District, Foshan City on the morning of 17 September 2018 was simulated at a 49m resolution in this paper. The structure of tornadic supercell and low-layer tornado-like vortex (TLV) are analyzed Using the mode data. Shearing wind helicity is introduced to diagnose the dynamic reasons for the formation of TLV. The results show that the tornado was produced by a supercell in the spiral rainband of typhoon Mangkhut. The supercell had the typical characteristics, such as hook echo, inflow notch, bounded weak echo region, and overhanging echo. The overshooting top, anvil and wall cloud can be seen on the vertical cross section of hydrometeor mixing ratio; The vertical circulation in the supercell is formed by updraft (UD) , front flank downdraft (FFD) and rear flank downdraft (RFD); TLV occurred between the low-level UD and RFD; The inside sank while the outside rose during the mature period of TLV; The diagnosis of the vertical vorticity equation indicates that the torsion term was more critical to the strengthening and upward spread of TLV during the developing period, while the stretching term dominated the changes in TLV during its mature period.