Abstract: To understand the impact of gas hydrate reformation on gas production efficiency and mining safety, a numerical model for hydrate reformation in vertical wells under depressurization was established using fluid dynamics and the finite difference method. The model simulated the location, region, spatiotemporal evolution, and quantity of secondary hydrate under different depressurization strategies. Results show that the hydrate dissociation front and the boundary of hydrate layers are the primary regions of hydrate reformation. Hydrate reformation of the hydrate dissociation front is usually earlier and greater accumulation further from the wellbore. The quantity of secondary hydrate initially decreases, then stabilizes and slightly increases in the middle stage, and finally increases due to insufficient heat supply. Different depressurization modes significantly impact hydrate reformation; step-wise depressurization (SD) can control the reformation range and delay the reformation time of the hydrate dissociation front compared to one-step depressurization (OD). The reformation quality of OD is inversely proportional to the depressurization decrement. Early-stage reformation quality of SD is inversely proportional to the depressurization decrement, while later-stage is directly proportional. These findings provide a theoretical basis for optimizing natural gas hydrate exploitation strategies.