The bank above water is usually high at low water level，and the force state of dragging the soft mattress with concrete interlock blocks to the riverbank of high elevation has not been studied. Aiming at this problem，the contact state between the soft mattress and the external environment is divided into three types by using the method of segmentation：clinging，hanging，and enwinding. The calculation formula of the static model in the clinging state，the calculation formula of the catenary model in the hanging state，and the calculation formula of the cambered surface friction model in the enwinding state are derived. The maximum dragging force of the soft mattress is analyzed and calculated，and the calculation method is obtained. The method can be applied in the analysis of soft mattresses in similar conditions for project design and equipment selection.