Gas hydrate exploration and drilling in the northern slope of the South China Sea have revealed a complex coexistence of gas hydrate and underlying shallow gas reservoirs. This coexistence area presents a promising target for future unconventional resource development and test production.This study aims to identify favorable target areas for high- concentration gas hydrate and shallow gas accumulations in sand- rich reservoirs in the Qiongdongnan basin. We use well log data and three- dimensional seismic data to characterize the spatial distribution of these reservoirsby spectral decomposition and RGB color blending techniques. Our findings show that sand- rich reservoirsare predominantly located within submarine fans located at the base of Quaternary mass transport deposits (MTDs). High gas hydrate accumulation sare locally observed at the top of gas chimney structures, which are controlled by high- flux fluid migration from deep sediments.Shallow gas, exhibiting multiplelayers, is trapped at the end of submarine fans and within channel- levee systems beneath the gas hydrate layer. This shallow gas acts as a significant source for overlying gas hydrate accumulation. Conversely, the formation of gas hydrate reduces sediment permeability, hindering upward gas migration and contributing to the enrichment of shallow gas reservoirs.Therefore, the Qiongdongnan basin presents favorable sand reservoir exploration targets characterized by the coexistence of gas hydrate and shallow gas. In addition, due to the changing of thickness of MTDs, local shallow gas anomaly area locate at the base of gas hydrate stability zone, creating conditions conducive to the formation of massive gas hydrate accumulations.This presents a highly promising target for future commercial development and exploration efforts.