Based on the ground observation data,ERA5 reanalysis data and Doppler weather radar data,a Pre-Tropical Cyclone(Pre-TC) squall line of typhoon Hato on August 23, 2017 was studied.The results show that:(1) the significant near-surface warming, warm and humid instability of the lower atmosphere and the CAPE above 2000J?kg-1 provide the early thermal conditions for the Pre-TC squall line; (2)the convective cells triggered near the surface convergence line and rapidly develops into a highly organized squall line, whose intensity and direction of movement were highly consistent with the convergence strength and location of the surface winds; (3)The configuration of low-level convergence and high-level dispersion of water vapor flux ensures efficient water vapor supply during the occurrence of short-term heavy precipitation. (4)The Doppler radar chart showed that the characteristics of mesoscale convergence zone in the vigorous stage of Pre-TC squall line was the most obvious , with multiple CR centers above 55dBZ and RIJ features; (5)When the convergence characteristics of wind directions on both sides of the squall line was weakened, the band structure broke up rapidly and the intensity diminished, the accompanying strong convective weather disappeared.