To optimize soil conditioning method and ensure the stability of excavation face and high efficiency of excavating, a good understanding of the mechanical behavior of conditioned soil in earth pressure balance (EPB) shield tunneling is essential. The pressurized vane shear apparatus was used to study the rheological behavior of conditioned soil from gravelly sand stratum. Results of undrained lateral confining compression tests revealed the relationship between the normal pressure and the compression strain of the foam-conditioned gravelly sand. Through vane shear tests, the shear deformation process of the foam-conditioned gravelly sand was investigated, and the peak and residual shear strength and corresponding effect factors were analyzed. Research results show that the foam-conditioned gravelly sand conformed to compressible non-Newtonian fluid. Therefore, constitutive model of compressible Bingham fluid for foam-conditioned gravelly sand was established based on rheology. The compressibility coefficient and rheological parameters (i.e., yield stress and viscosity) of the conditioned soil were obtained by fitting the test results. The pressure dependence formulas of density, peak and residual rheological parameters were proposed. The research can enhance the understanding of the mechanical behavior of foam-conditioned gravelly sand, and provide a theoretical basis for computational flow simulation to accurately reflect the macroscopic movements of conditioned soil in EPB shield tunneling.