The flexible mattress is the main beach protection structure in the middle and lower reaches of the Yangtze River，the strain response characteristics of its deformation are important for evaluating and analyzing the service state of the flexible mattress，there are few studies on this.To address the current difficulties in the study of the strain response characteristics to the subsidence deformation of flexible mattress，we carry out the model experiments，and study the strain response characteristics under the subsidence deformation of flexible mattress to propose the identification method of subsidence deformation.The results show that the section strain response to the subsidence deformation of the flexible mattress can be characterized as “bimodal” distribution.This distribution feature is formed by the internal mattress bending and coiling inward，driving the fiber under pressure through the fixation at the fixed point，resulting in a negative strain in that part of the sensing fiber.