Abstract: At present, only China and Japan have implemented production test of offshore gas hydrates. The problems and lessons encountered in Japan shall be helpful to the hydrate research and development in China. The deployment, gas production, problem and research in Japanese two production tests completed in 2013 and 2017 in Nankai Trough were summarized, and the gas production of three production wells in two tests were compared. It was found that the two tests failed in solving the problem of the difference between actual and predicted gas production results, for which the characteristics and physical properties of hydrate reservoirs should have been the key issues. In addition, the production of hydrates is so complicated that sand control, decompression, drainage, etc., must be considered comprehensively, and balance between various production parameters required for stable production should be compromised.