Abstract: Rationale drilling planning requires precise data on gas hydrate reservoir and its depth before drilling. 2-D seismic data from the Northern South China Sea were used to identify the top and bottom of the gas hydrate reservoir by the changes in velocity and impedance. The depth of the reservoir was then calculated with RMS velocity. Guangzhou Marine Geological Survey carried out field drilling in 2007, and the gas hydrate reservoir with high saturation was discovered at the depth predicted, suggesting that the calculation is precise enough for drilling planning.