In deepwater fields, drilling costs are extremely high, and the “one sand, one well” situation is common, in which a single well must control an overly large area of the gas field. Structural accuracy decreases in areas distant from the well locations, making gas reservoir prediction and sand body delineation challenging due to the limited resolution of seismic data. To address these challenges, this study applied high-precision full-waveform inversion (FWI) velocity modeling and broadband imaging technology in a deepwater exploration of the South China Sea. In the preprocessing stage, based on the geological challenges and features of the acquired seismic data, we selected appropriate signal-processing methods and optimized the algorithms and parameter sets, successfully developing a customized broadband processing workflow specifically tailored for deepwater applications. The entire broadband processing sequence effectively supported subsequent FWI modeling. During the imaging stage, FWI was successfully applied for the 1st time in the deepwater of the South China Sea. Together with Q pre-stack depth migration, this integrated approach effectively addressed challenges in structural depth prediction and significantly improved imaging resolution. This study provided real-time support for gas field development and optimized the well placement for deepwater development.