Atmosphere-controllable small backflow type wind tunnel experiment device and working method thereof

The invention relates to an atmosphere-controllable small backflow type wind tunnel experiment device, which comprises a wind tunnel main body, a gas distribution system and a measurement and control system, the wind tunnel main body is a concentric-square-shaped circulation path and is formed by connecting a stable section, a contraction section, a test section, a first diffusion section, a first corner, a second diffusion section, a second corner, a transition section, a power section, a third diffusion section, a third corner, a fourth diffusion section and a fourth corner end to end; a wind speed sensor and a temperature sensor are arranged on the test section; the gas distribution system is composed of an upper gas distribution subsystem and a lower gas distribution subsystem, the upper gas distribution subsystem and the lower gas distribution subsystem respectively comprise a gas cylinder, a pressure reducing valve, a switch valve, a gas mass flow controller and a two-position three-way valve which are