Abstract: The strain transfer efficiency between flexible mattress and optical fibers is key to monitor the deformation of flexible mattress by applying optical fiber sensing technology. The purpose of this paper is to investigate the strain transfer efficiency between flexible mattresses and optical fiber sensors during deformation of flexible mattresses and its influence on the measurement accuracy. Theoretical analysis and experimental study show that under linear tensile conditions, the strain can be efficiently transferred from the mattress to the optical fibers, and the region below the low transfer efficiency line is mainly located at the edge of the optical fibers; whereas under bending deformation conditions, the deformation measurement error is linearly correlated with the relative fixed-point spacing R, and the average error of the measurements is within-4% when R=1.2, and the range of the measurement error is between-15% and-30% when R=2.4～4.8. The research results of this paper can provide a reference for the measurement technology of river engineering model tests and the field application of optical fiber sensing to monitor the deformation of flexible mattresses.