Natural gas hydrates (NGHs) are a new, clean, and effective energy source with great potential for exploitation. The efficient exploitation of NGHs has been a focus of research worldwide. Water migration in hydrate sediments is an important parameter influencing NGH exploitation. However, there is still little research in terms of visualization studies on the variation of hydrate distribution during the water flow process in hydrate-bearing sediment. Such variation of hydrate distribution and the influence of water migration on methane hydrate (MH) dissociation with different backpressures and water flow rates were systematically and visually analyzed in this study, where the influence of temperature and pressure variation on MH dissociation was completely eliminated. The results showed that the chemical potential difference between the hydrate phase and the aqueous phase caused MH dissociation during the water flow process and that the rate of MH dissociation increased with decreasing backpressure and increasing water flow rate. When the rate of MH dissociation is low, there will be a longer time for the flow channel to appear, vary, and disappear. Based on this conclusion, a new method of water flow erosion to improve NGH exploitation is proposed in this study.