Abstract: The dynamic shear modulus decay of calcareous sand treated by microbially induced calcium precipitation (MICP) across a wide shear strain range was investigated using resonant column and dynamic triaxial tests, with variations in calcium carbonate precipitation content (C_Ca) and effective confining pressure (σ_c). Prediction formulas were proposed for the maximum dynamic shear modulus (G_max) and the reference shear strain (γ_r), considering both σ_c and C_Ca. Based on the Hardin-Drnevich model, a predictive model was established for the dynamic shear modulus decay curve. Results indicate that the Hardin-Drnevich model accurately describes the G/G_max decay behavior of MICP-treated calcareous sand. Moreover, the curvature coefficient ζ exhibits limited sensitivity to variations in σ_c and C_Ca. An empirical method is presented for determining ζ in MICP-treated calcareous sand. Both G_max and γ_r exhibit a linear relationship with C_Ca, while their relationship with σ_c is described by a power function and a linear function, respectively. A model that considers both σ_c and C_Ca for predicting the dynamic shear modulus decay curve was developed, grounded in the Hardin-Drnevich model. The applicability of this model was validated.