Microbially induced calcite precipitation (MICP) is a promising technology for soil improvement, where the treated soil can be regarded as the structural one. In this study, a micromechanics-based model is proposed to investigate the mechanical behaviors of inherently anisotropic MICP-cemented sand, which consists of a hexagonal close-packed (HCP) particle assembly (2D) composed of bonded elliptical particles with same size. A size-dependent bond failure criterion is adopted to define the microscopic mechanical reactions between the particles to model the nonlinear characteristics of the soil. Based on the homogenization theory and lattice model, the stress-strain relationship, strength criteria, and corresponding macroscopic mechanical parameters with respect to microscopic parameters for MICP-cemented sand are derived and verified by DEM simulation based on the regularly arranged particle assembly. The effects of key parameters, including cement content, initial void ratio, inherent anisotropy, and confining pressure, on the mechanical behaviors of MICP-cemented sand is investigated in detail, and the good agreement between the theoretical solution and laboratory test results validates the applicability of the theoretical solution for analyzing MICP-cemented sand.