The invention relates to a natural-gas hydrate three-dimensional experimental device and a three-dimensional simulated experimental method, which can be used for freely changing experimental boundary conditions and have changeable boundary conditions. The experimental device comprises a three-dimensional reaction kettle, a temperature and boundary control unit, an inlet control unit, an outlet control unit and a data processing unit; and the three-dimensional reaction kettle is arranged in the temperature and boundary control unit. Through the natural-gas hydrate three-dimensional experimental device and the three-dimensional simulated experimental method, experimental temperature-boundary conditions can be freely changed; the natural-gas hydrate three-dimensional experimental device and the three-dimensional simulated experimental method are applicable to the three-dimensional reaction kettles in various sizes; a three-dimensional hydrate physical-simulating device can be amplified onto an unlimited earth layer from a limited laboratory scale; and the formation temperature gradient and the surrounding-heating exploiting mode can be simulated.