The composite early strength soil stabilizer (CRSS) has the characteristics of rapid setting and high strength. The independently developed CRSS stabilizer is used to rapidly solidify the surface sludge as the overlying hard shell layer. Through model tests, the failure mode of the hard shell layer, p-s curve characteristics, the shape of the deflection basin and the distribution law of soil pressure under different overlying hard shell layer thicknesses (3 cm, 6 cm, 9 cm and 12 cm) are studied. On the basis of the existing deformation theory of the deflection basin, combined with the test results, deformation shape function of the deflection basin is modified. The results show that with increase of the thickness of the hard shell, the failure mode of the hard shell transits from folding failure to punching failure; The greater the thickness of the hard shell, the more obvious the diffusion effect, and the higher the ultimate bearing capacity, as well as the corresponding increase in settlement; the settlement displacement at different distances from the central point of the load plate can be described by the shape of the deflection basin. A modified formula for calculating the assumed deformation of the logarithmic deflection basin is proposed, which is more reasonable than the formula for calculating the assumed deformation of the linear deflection basin; the earth pressure decreases from the center outwards and gradually decreases along the depth direction; the distribution of earth pressure becomes more uniform with increase of the thickness of the hard shell.