In order to solve the difficulty in predicting tunnel deformation induced by surface surcharge in composite strata and reveal the strain response mechanism under sand-clay interbedded conditions, a combination of laboratory reduced-scale model tests and ABAQUS numerical simulations was used to investigate the tunnel deformation patterns and load-strain relationships under different load levels. The results show that the strain variation at the loading point is most significant with the increase of the upper load. An attenuation trend is observed with increasing distance. Strain inflection points and arching phenomena appear in the mid-span region due to soil stress redistribution. The tunnel deformation in clay is significantly greater than that in sand. The stress distribution is significantly regulated by tunnel geometric parameters. It is concluded that the traditional homogeneous strata assumption is overcome. The mechanisms of load transfer and tunnel deformation under soil anisotropy are revealed. The strain evolution trend at critical points is effectively predicted by the established load-strain equation. A theoretical basis is provided for the safety maintenance of deep-buried tunnels in complex soil conditions.