With the development of deepsea natural gas hydrate resources, cementation technology has become crucial for ensuring the safety of extraction operations. Controlling hydration heat in cement slurry is vital for preventing hydrate decomposition and maintaining wellbore stability. Currently, the application of microbial technology in cement slurry has made preliminary progress, especially in improving the mechanical properties of the cement slurry. However, research on controlling hydration heat is still relatively scarce.This study focuses on the potential of microbial cement slurry in reducing hydration heat and explores its application prospects in deepwater hydrate formations. Hydration heat tests, thermogravimetric analysis (TGA), fouriertransform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energydispersive spectroscopy (EDS) were used to investigate the influence mechanism of microbial mineralization on the hydration heat and hydration products of cement slurry. Our findings reveal that microbial cement slurry significantly reduces hydration heat, particularly in the midtolate stages of hydration, with a 13. 19% lower cumulative heat release compared to the control group.The calcite produced by microbial mineralization effectively suppresses cement hydration, delaying the hydration heat peak and continuously reducing the hydration rate during the process. Moreover, microbial cement slurry exhibits higher free water and hydrated calcium silicate gel content, while exhibiting lower calcium hydroxide content compared to the control group. There is an optimal calcite content (around 3. 0%) for minimizing hydration; exceeding this threshold leads to a decrease in heat reduction.This research provides innovative solutions to the challenge of gas hydrate decomposition caused by the exothermic reaction of cement slurry hydration in deepwater hydrate layers. It holds significant implications for developing cement slurry systems capable of withstanding the demanding conditions of the open ocean.