<p>Microbially induced carbonate precipitation (MICP) offers a promising approach for reinforcing gas hydrate-bearing sediments, owing to its low exothermicity, good injectability, fast reaction kinetics, and ability to maintain permeability after treatment. In this study, a high-pressure microfluidic platform was used to simulate in situ hydrate conditions and investigate how microbial mineralization affects hydrate stability. The spatial distribution, cementation modes, morphology, crystal types, and quantitative characteristics of calcium carbonate precipitates were analyzed, and their stability during hydrate dissociation induced by depressurization was also evaluated. Results showed that injection of microbial solutions led to localized hydrate dissolution, while subsequent mineralization triggered further decomposition. Although <i>Sporosarcina pasteurii</i> successfully precipitated calcium carbonate under gas hydrate-bearing sediments, the hydrate distribution significantly influenced the crystal deposition patterns. In addition to conventional cementation modes, new modes were observed, including particle-hydrate bridging, hydrate surface coating, and pore filling within hydrates. Spherical crystals of two distinct sizes were identified, both consisting of vaterite and calcite. Gas release during hydrate decomposition changed the fluid flow paths and temporarily reduced mineralization efficiency. However, mineralization efficiency improved with increasing injection frequency and cementation solution concentration. During depressurization at 0.02&#xa0;MPa/s, 86.34% of the precipitated calcium carbonate remained attached, and gas–liquid migration was identified as the main factor controlling crystal detachment. These findings provide new insights into the coupled dynamics of MICP and hydrate systems, supporting the potential of MICP for mechanical stabilization of hydrate reservoirs during production.</p>