Natural gas hydrate，which deposits on the ocean floor or in permafrost regions in vast quantities, is a potential future energy resource. The method by depressurization is known to be adopted for large scale exploitation natural gas hydrates. The heat transfer boundary can affect overly hydrate dissociation rate. Investigated these control mechanisms, built one two-dimensional model, and analyzed the change of temperature,pressure,hydrate saturation and cumulative gas produced under the influences of different heat transfer boundary conditions. The calculation results show that natural gas hydrates exploited by depressurization need heat transferred from surroundings. The amount of gas produced at adiabatic condition is only 1/36 to that of gas produced in complete decomposition. With higher temperature at boundary, hydrate decomposes more rapidly, decomposition rate at boundary temperature 277.45 K is 2.5 times as much as that at 275.45 K, and gas generated rate is greater, but the magnitude of heat makes a minor effect on cumulative gas produced.