In order to improve the reinforcement effect of microbially induced calcium carbonate precipitation (MICP) technology on sand, the test of MICP-treated sand reinforced by pozzolan was designed and carried out considering the porous structure and activity characteristics of pozzolan. The enhancement effect and enhancement mechanism of pozzolan on the MICP-treated sand were systematically analyzed by integrating macroscopic physical and mechanical tests and microscopic tests. The results showed that: 1) Pozzolan could significantly improve the bacteria fixation rate and cementation material production in the process of sand microbial reinforcement, and the optimal amount of pozzolan content was around 10%, which increased the bacteria fixation rate by 118.28% and the cementation substance production by 29.55% compared with the conventional MICP. 2) The addition of pozzolan greatly improved the compressive strength and resistance to deformation of bio-cemented soil. Under different confining pressures, the compressive strength of the bio-cemented sand increased by 52.26%−62.96%, and the strain at failure increased by 100.00%−112.58%. 3) After the addition of pozzolan, the pore size and void ratio of the bio-cemented sand were decreased obviously, and the overall compactness and impermeability performance were further improved, with the void ratio decreased from 20.12% to 14.17% and the permeability coefficient reduced by an order of magnitude. 4) The enhancement mechanism of pozzolan on MICP-treated sand mainly included three aspects: for one thing, the pozzolan played a good filling effect between the sand particles, which significantly reduced the large pores between the particles and increased the compactness of the sample; for another, the good adsorption of pozzolan effectively increased the content of bacteria in the sample, which increased the production of calcium carbonate and enhanced the uniformity of distribution; on the third hand, the active substances in pozzolan participate in the reaction to generate gelling substances and calcium carbonate crystals to form a composite gel, which could further enhanced the cementation properties and compactness of the bio-cemented sand.