The invention relates to a visual reaction kettle and a visualized experimental system and method for replacing natural gas hydrate. The reaction kettle used by the system comprises a barrel, a front flange, a rear flange and glass; the front flange, the rear flange and the barrel are each of a hollow structure, the glass is embedded on the hollow structure of the front flange and the hollow structure of the rear flange respectively, and the front flange, the rear flange and the glass are used for sealing the barrel; the barrel is provided with multiple connectors; the system comprises a sampling tank, a vacuum pump, a first natural gas bottle, a carbon dioxide gas bottle, a second natural gas bottle, an environmental climate case, a beaker, a sensor, an image acquisition device and a data acquiring and processing device. By means of the experimental system, the process of replacing the natural gas hydrate with carbon dioxide at different phase states can be carried out, macroscopic thermodynamic and dynamic data in the replacing process is obtained, and meanwhile the dynamic characteristics, the heat-fluid-solid coupling phenomenon and the hydrate form change in the replacing process are recorded; the visual reaction kettle and the visualized experimental system and method for replacing the natural gas hydrate can be used for observing the natural gas hydrate generation phenomenon.