One of the critical challenges in the retrieval of three-dimensional wind fields in precipitation systems is the accurate estimation of the final falling velocity (Wt) of precipitation particles. To assess the ability of dual-polarization radar in estimating Wt, the relationship between Wt and dual-polarization radar in the S and X bands is established in this paper based on the raindrop spectrum data collected from the Longmen Area of Guangdong Province. This relationship is then applied to the wind field retrieval of the Guangzhou and Shaoguan radars. In addition, an experiment is conducted to invert a squall line event that occurred in South China in April 2019. The wind field structure of the squall line process is analyzed, and the difference in the wind field structure of Wt in retrieval performance is estimated by different methods. The results indicate that the functions of Wt estimated by S and X band radars using echo intensity (ZH) and differential reflectivity factor (ZDR) are in the forms of a power function and a primary function, respectively. The root mean square error of Wt estimated by ZDR is smaller than by ZH, and the correlation coefficient is larger, which suggests that it is better to estimate Wt by ZDR. The squall line process primarily developed from northwest to southeast, with the wind field dominated by westerly and southwesterly winds. There was a distinct convergence zone in the arcuate echo area in the front of the squall line, which had a perpendicular structure with low-level convergence and high-level divergence. Compared to the three-dimensional wind field obtained by estimating Wt with different methods, the changes in the horizontal wind field are primarily concentrated in the range of ±1 m·s-1. Specifically, the change in horizontal meridional wind speed (Δu) is mainly positive, while the variation of horizontal zonal wind speed (Δv) is negative. In the vertical direction, the wind speed (Δw) varies within ±0.15 m·s-1, but is positive on the whole. Additionally, the values of Δu, Δv, and Δw in lower levels are smaller than in higher levels. These research findings could offer valuable references for retrieving the three-dimensional wind field and vertical velocity of precipitation systems.