Marine gas hydrated formation is often porous and permeable. Drilling fluid will inevitably exchange the energy and materials there during the drilling process. The intrusion of water-based drilling fluid into hydrated formation and hydrate decomposition due to heat transfer by temperature difference are coupled together. The intrusion can be described as non-isothermal and unsteady percolating diffusion processes with phase transition. On the basis of comprehensive analysis on the characteristics of drilling fluid intruding natural gas hydrate-bearing formations and according to the numerical simulation of gas hydrate exploitation and conventional oil and gas reservoirs drilling fluid intrusion model, one-dimensional model of drilling fluid radial intruding into natural gas hydrate-bearing formations was established. By using the program, the analysis was made on formation pressure, saturation of each phase and the distribution of temperature while drilling fluid intruding into hydrate-bearing formation.