Abstract: Mud volcanoes in different sizes are found associated with gas seepages in the northeastern South China Sea. Restricted by types and low resolutions of the data, there are gaps in the size of mud volcanoes. Using multi-beam bathymetry data, we find 27 new mud volcanoes in the study area 5~120 m in heights with diameters between 300~1 170 m. Most of them are found in the canyons of heavy erosion. There are enough mud and gas as sources, and the overpressure system due to the joint actions of rapid sedimentation rate and tectonic compression forced the gas-rich mud to pierce into the thin canyon deposits and form mud volcanoes.