Mechanisms and evolvement of gas hydrate (GH) reservoirs is the key to clarify profitable gas resource, a kind of dynamic cycling process of GH reservoirs has been investigated. Phenomena pertinent to formation and decomposition of GH deposits have been obtained. Environmental alteration affects significantly existence and occurrence of hydrate deposits. Formation and decomposition of hydrate in sediments determines accumulation and morphology of hydrate-bearing sediments. Formation and decomposition of GH can occur simultaneously. Gas transport in seafloor sediments continuously happens vertically and laterally from free gas to hydrate circularly. Relic hydrates enwrapped by ice on surface in hydrate metastability zone(HMZ) release volumes of gas more than available pore volume locally in permafrost. These facts all verify a kind of dynamic cycling process on GH deposits.