In order to explore the coupling transfer mechanism, a multi-layer mechanical model of sensor components is constructed. The surface-mounted strain transmission coefficient formula is derived by analysing the influence between structural parameters and strain transfer coefficient. The strain transmission coefficient of the sensor structure has a positive exponential relationship with the elastic modulus of the tested material through modelling, and the growth trend is gradually reducing. The gypsum material curve is in a parabola, and the top point is 87%. The curved form of concrete and low-carbon steel materials is the same, the top point is 100%, and the concrete curve of the three strengths is close to coinciding. Through integral calculation, the average strain transmission coefficient of gypsum material is 73.5%, C20 concrete is 94.7%, C30 concrete is 95.1%, C50 concrete is 95.3%, and low-carbon steel is 97.1%. The matrix diameter negatively correlates with the strain transmission coefficient, but the influence is small. Integrating the strain transfer coefficient curve, the average strain transfer coefficient of 1.0 mm matrix diameter is 97.45%, 1.5 mm matrix diameter is 97.38%, 2.0 mm matrix diameter is 97.30%, and 2.5 mm matrix diameter is 97.25%. The 3.0 mm matrix diameter is 97.21%. Experiments have verified the rationality of the theoretical formula and the correctness of the influence relationship, which provides a reference for the application of fiber grating sensing technology in tunnel structure monitoring.

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