Abstract: The macro-physical and mechanical properties of clay are closely related to its micro-particle shape. The typical soft clay in Tianjin Port area of China is taken as the research object, and its particle shape characteristics are analyzed and studied by the digital image technology. The main conclusions are as follows: (1) The ratio of long to short diameter of soil samples is mainly concentrated between 1 and 2, and the ratio of soil particles gradually decreases with the increase of fine particle content. Moreover the slender particles gradually decrease, and the soil particles tend to be regular. (2) The roundness of soil samples mainly concentrates between 0.9~1.0, and the finer the particles, the larger the overall roundness of soil samples, the more rounded the shape of soil particles. (3) The fractal dimension of the surface roughness of clay, silty clay and silt is 0.9590, 0.9574 and 0.9654, respectively, which indicates that the finer the soil particles are, the smaller the surface fluctuation is and the smoother the surface is.