To explore the mechanical properties of the flexible mattress in the process of counter flow sinking，based on the mechanical properties that the geotextiles can only withstand tensile stress and the geometric nonlinear deformation characteristics of the mattress，we establish the nonlinear finite element model of the flexible mattress by the nonlinear shell element Shell181 to simulate the geotextiles，and verify the the accuracy of the model by comparing with the catenary theoretical calculation results. We analyze the influence of the simplified concrete block modeling method in the existing research on the calculation results，and carry out the nonlinear finite element numerical simulation of the counter flow sinking process of Zhangjiazhou head after improving the construction process by the verified model. The results show that the maximum tension of the mattress appears within the range of 1 m on both sides during sinking process，and the lateral reinforcement bar with the length of 4 m on the edge of the mattress can effectively reduce the risk of tearing. The tensile safety factor of geotextiles and reinforcement bar is greater than 2，the displacement of flexible mattress is small，and the construction scheme is safe and effective.