Abstract: Resource assessment of gas hydrates is a basic requirement to hydrate exploration. It concerns not only the future energy supply, but also the possible impacts on global climate change and natural geohazards the exploration may induce. The selection, improvement and development of appropriate methods remain critical for the improvement of the quality and credibility of the assessment results. Based on the review of concerned researches abroad and at home, we discussed in this paper the definition of the gas hydrate resources and reserves. 4 methods were summarized according to the principles of gas hydrate generation and accumulation models. Also discussed are the experiences accumulated so far in gas hydrate resource assessment and their implications for China. The study suggests that the assessment should be done upon a comprehensive understanding of the generation and accumulation of gas hydrate and the changing trends of concerned factors so as to obtain the effective assessment parameters. All the available information of geophysics, logging and well data should be fully used to define fine structures and depositional characteristics of the exploration targets for improvement of the credibility of the assessment results.