<p>Internal erosion of gap-graded sand is one of the most common causes of hydraulic infrastructure failures worldwide. Microbially induced carbonate precipitation (MICP) deposits calcium carbonate on particle surfaces and within pores. This process has the potential to control internal erosion by filling and bridging pores. In this study, the hydraulic conductivity of MICP-treated sand was measured and calculated to elucidate the effects and mechanism of MICP on the permeability of sand. A series of internal erosion tests were conducted using a one-dimensional column test apparatus. During the internal erosion process, pressure gradient, cumulative erosion weight of particles, and flow rate were measured. The critical hydraulic shear stress and erosion rate coefficients were analyzed to identify potential susceptibility to internal erosion. An energy-based method was used to categorize erosion sensitivity ranging from highly erodible to highly erosion-resistant. The results indicate that MICP treatment can significantly reduce hydraulic conductivity, with reductions of up to 80% after three treatment cycles at a cementation solution concentration of 1.0&#xa0;mol/L. After MICP treatment, the erosion resistance index increased for all three soil samples, indicating that MICP is effective in enhancing the soil’s erosion resistance. The critical shear stress (<i>τ</i>_c) serves as a strong indicator of erosion resistance, while the decrease in the erosion coefficient (<i>α</i>) reflects reduced sensitivity to shear stress and enhanced resistance to erosion. Among the influencing factors, the number of treatment cycles has the most significant impact on the erosion resistance index, followed by the cementation solution concentration, whereas the fine particle content (20~40%) has a relatively minor effect. These findings provide a valuable reference for preventing failures of hydraulic infrastructure caused by internal erosion.</p>