Abstract: A large number of sand waves and sand ridges are developed in the waters southwest of Dongfang, Hainan, which seriously affects the safety of underwater engineering. In order to know the seabed landform and micro-geomorphological characteristics in the waters, side-scan sonar and shallow-stratum profiler have been used for the detection. The results show that sand waves and sand ridges are very developed in the study area. Due to the influence of these geomorphological units, the water depth in the study area varies significantly and the terrain conditions are complex. Based on the morphology and scale of the developed sand waves, six geomorphological types are identified, which include sand ridges, giant sand waves, large sand waves, medium sand waves, small sand waves and sand ripples. Based on the development characteristics of the sand waves and sand ridges and their spatial combination relationships, it can be inferred that the sand ridges were developed in a high-energy environment of shallow water in the period of low sea level and are in a state of weak activity, whereas the sand waves were mainly formed in a high-sea level and low-energy environment since the last sea transgression and are still in the process of development. These results can provide references for the design and protection of ocean prohects such as submarine pipeline and pile foundation.