Abstract: The marshy and lacustrine clay, which is of special engineering properties different from other soft clays, formed in the special sedimentary environment that lakes and marshes were drying and shrinking due to climate change. To investigate the engineering geological characteristics of the marshy and lacustrine clay in the Hengshui Lake area, the sedimentary environment, sedimentary history, distribution characteristics and stratigraphic structure of the marshy and lacustrine clay are discussed respectively. Moreover, the physico-mechanical indexes, mineral compositions, particle size distribution and microstructure features of the marshy and lacustrine clay are compared with other soft clays. The results show that the physical indexes of the marshy and lacustrine clay are close to or reach the soft clay, but the mechanical indexes of the marshy and lacustrine clay are better than those of the soft clay. When the stress level in soil exceeds the structural yield stress, the strength and compression of the marshy and lacustrine clay will abruptly change since the marshy and lacustrine clay possesses significant structural properties. The content of colloidal particles in the marshy and lacustrine clay is 39%, which is obviously higher than other soft soils. Meanwhile, high content of magnetite in the marshy and lacustrine clay, which makes it easy to forms iron oxide cements, enhances the cementation characteristics of soil, resulting in forming a more stable structure skeleton. It can be seen that the mismatch between physical indexes and mechanical indexes of the marshy and lacustrine clay is responsible for its special mineral compositions and microstructures. The difference in soil particle morphology, soil particle contact and microstructure are greatly responsible for the difference in the engineering geological characteristics between the and lacustrine clay and soft soils in other areas.