The foundation soil of the Shanghai Binhai Plain is covered with the fourth layer of gray muddy clay, with a thickness of 5-10 meters, which is the main weak soil layer. For clays with obvious rheological characteristics, secondary consolidation deformation cannot be ignored, and it is the main cause of post-construction settlement. In order to study the secondary consolidation of this layer of soil, a secondary consolidation test of 10 groups of undisturbed soil samples was carried out. The test showed that the secondary consolidation coefficient of this layer of soil was between 4.14*10-3 and 9.88*10-3, and at the same time The ratio of the ratio to the compressibility index ranges from 0.017 to 0.028, indicating that the secondary consolidation coefficient and the compressibility index are basically linear. The research results have certain guiding significance for the understanding of the secondary consolidation characteristics of the muddy clay in the fourth layer.