The invention relates to an experimental device for generating a longitudinal hydrogen concentration gradient in a closed cabin. The device comprises the closed cabin, a gas storage tank, a gas distribution mechanism and a data acquisition mechanism; spray heads are uniformly distributed at the top of the closed cabin; gas concentration sensors are uniformly distributed on one side surface of theclosed cabin from top to bottom; the lower part of the closed cabin is provided with an exhaust hole; the gas distribution mechanism comprises a gas distribution pipe, a vacuum pump, a hydrogen tank and an air tank; and the data acquisition mechanism comprises a data module and a computer. During an experiment, the exhaust hole in the lower part of the closed cabin and the spray heads at the top of the closed cabin are opened for uniformly spraying hydrogen into the cabin and discharging original air in the cabin to always keep one atmospheric pressure in the cabin; the exhaust hole is closed,and the hydrogen is diffused in the cabin to form the longitudinal hydrogen concentration gradient; and the gas concentration sensors are used for detecting real-time oxygen concentrations in different positions, and due to the fact that the air pressure in the cabin is kept unchanged, the increased hydrogen concentration is namely the reduced oxygen concentration. According to the device, the blank of longitudinal concentration gradient research of combustible gas of the closed cabin in combustion explosion characteristic research of the combustible gas is made up for.