The invention relates to a stratum stability simulating device and particularly relates to a three-dimensional simulating device of natural gas hydrate mining stratum stability. The three-dimensional simulating device comprises a three-dimensional model, an axle load control unit, an environment control unit and a post processing unit, wherein an inner cavity of the three-dimensional model is separated into a sealed simulating cavity and a sealed axle load sealing cavity by an axle load sealing piston arranged in the inner cavity, and a vertical well and a horizontal well, which stretch into the simulating cavity, are arranged on the three-dimensional model; the three-dimensional model is located in the environment control unit; and a plurality of sensors are arranged on the three-dimensional model, the axle load control unit and the environment control unit, and the sensors are electrically connected with the post processing unit. The simulating device disclosed by the invention can truly simulate the external environment and combine in situ synthesis and decomposition of hydrate with stratum stability, thereby achieving high reliability and high accuracy and comprehensively evaluating the mechanical property change of the stratum and the stratum stability in a mining process to provide guidance to natural gas hydrate mining.