Abstract: The site survey data collected from the 109 wells in the Chengdao sea area indicate that the seabed of the study area is rather smooth. Erosional and mottle landscapes, and residual platforms occur only in local waters. Surface sediments of the study area are composed of silt, silty clay, soft silty clay and mud. The study area, based on water depth, geomorphology, spatial distribution and engineering geological properties of the bottom sediments of the 109 well sites, could be divided into four zones. Engineering suitability for pile boots and deep pile platform was evaluated for the zones. Results show that the first, second and fourth zones are suitable for big pile boots and platforms. As to the third one, further work, such as penetration testing, is required before the drilling platform to be constructed. And the area near slopes and ridges should be avoided. All the four zones are suitable for deep pile platforms if the foundation is deeper than 20~30 meters.