<p>Adding basalt fiber (BF) to phosphogypsum (PG) can effectively solve its inherent defects such as low early strength, high brittleness and poor water resistance. Most existing studies focus on macro mechanical tests, making it difficult to observe the evolution of mesoscopic structures, and the mesoscopic numerical model of the BF/PG interface is not mature. To address this, this study modifies the constitutive model of PG-based materials to adapt to the concrete damaged plasticity (CDP) model, solving the problem of computational non-convergence, and then establishes a two-dimensional mesoscopic model to analyze the influence of BF on the damage evolution of PG-based materials. The results show that BF can effectively inhibit the damage of PG-based materials by forming a bridge across the crack to transfer tensile stress and hinder crack propagation; the higher the fiber content, the more obvious the inhibition effect, while the influence of fiber length on damage inhibition shows a trend of first enhancement and then weakening. Increasing BF content can improve the compressive strength of PG-based materials, and the influence of fiber length on compressive strength is first increasing and then decreasing; BF has no significant effect on the elastic modulus of PG-based materials, but it can effectively improve the ductility and inhibit crack expansion, enhancing the deformation capacity before material failure. This study provides theoretical support for optimizing the BF mixing process and establishing a macro performance prediction model, promoting the high-value and green utilization of PG.</p>