Abstract: Ningde City is located in the north of Fujian Province. Its soft clay has typical sedimentary characteristics of Quaternary soft clay in Northeast Fujian,and its unique sedimentary environment makes it different from the traditional Zhejiang-Fujian coastal soft clay in physical and mechanical properties. Based on the geological survey,including in-situ and laboratory geotechnical tests surrounding Sanduao,the sedimentary characteristics,physical and mechanical properties of the soft clay in Ningde are systematically investigated. It is found that the clay has the characteristics of high compressibility,high liquid limit and high sensitivity,and is vulnerable to be disturbed. Attention should be paid to the loss of strength in engineering construction and evolution of infrastructure disaster. The abundant diatom with flourishing pores and strong hydrophilicity is the reason of the high specific surface area and its structural characteristics. These two remarkable features distinguish Ningde soft soil from other traditional soft clays.