Two profiles of refraction and wide-angle reflection were completed in the Yinggehai Basin using ocean bottom hydrophones (OBHs) as receiver. These profiles reveal a low velocity layer (LVL) to the west of No. 1 Fault in the basin, with velocity of 3.0–3.5 km/s. Its upper interface lies at 3.5 km below the sea bottom at the NE end of the profiles, and deepens southwestward to 4.6 km near the axis of the basin. It coincides with the top of a gas-bearing, high-pressure layer defined by well logging. This suggests that the LVL is a layer of less-compacted and gas-charged sediments. The lower interface of the LVL is about 9 km in depth. Sediments above the LVL have velocity varying from 2.0 to 4.1 km/s. The acoustic basement is found only east of No. 1 Fault, with velocity of 5.8–6.2 km/s. A NNW-SSE-running OBH seismic profile across the Xisha Trough was completed on the same cruise. Moho and other deep interfaces are clearly visible in the profile.