The global investigation of natural gas hyate (NGH) has made rapid progress, and at least 30 groups of scientists have carried out quantitative evaluation of NGH resource potential since 1973. Based on the academic thought of Whole Petroleum System , Professor Pang Xiongqi and others combined the formation and distribution of natural gas hydrate with conventional oil and gas and unconventional oil and gas, and established a quantitative relationship model between them based on the idea of mass balance. Under the constraints of the main control factors and the actual test data, the global natural gas hydrate recoverable resources quantity is calculated as 41.46×1012 m3. Based on the principle of mass balance, there are seven main controlling factors to calculate the recoverable resources of global natural gas hydrate. It includes the area of the free hydrocarbon dynamic field (AF-HDF), the thickness of the free hydrocarbon dynamic field (HF-HDF), the area of the hydrate stability zone (AGHSZ), the thickness of the hydrate stability zone (HGHSZ), the amount of conventional oil and gas resources (Qc1), the amount of heavy oil asphalt resources (Qc2) and the recovery coefficient (RGH). Taking into account both the biological degradation and thermal degradation mechanisms of hydrates, the source rock gas supply ratio (g) is introduced considering the difference in volume coefficients between hydrates and conventional oil and gas, their respective volume coefficients Bgh and Bg are introduced. In the case that the principle of the method is completely correct, the sensitivity and reliability of the numerical simulation results need to be analyzed considering that there are many influencing factors and their respective variation ranges are large. In this paper, the sensitivity of the mass balance method to obtain the assessment results of global NGH recoverable resources are studied. The results showed that the recoverable coefficient exhibits the highest sensitivity (31.13%), followed by Qc1, Qc2, AF-HDF, AGHSZ, HGHSZ and HF-HDF, with values of 22.70%, 13.38%, 12.44%, 8.89%, 6.12% and 5.34%, respectively.Then under the joint control of all factors, applying Monte Carlo simulation to assess credibility.The global mode and mean values of recoverable hydrate resources are 78.09×1012 m3 and 86.06×1012 m3 respectively, and the confidence of ±50% before and after the key value is 88.95%, indicating a high reliability. Simultaneously, validation was conducted based on the assessment results of previous researchers. The effective method to further improve the accuracy of global hydrate recoverable resources evaluation is to obtain more actual test production data and reduce the uncertainty between them.