The invention provides an opening and closing dual-purpose low-speed return flow tunnel. An experimental section is divided into a bottom plate and an upper cover; the bottom plate is fixedly arrangedon the ground, and the upper cover and the bottom plate are in buckling fit to form the experimental section; the upper cover can move on the bottom plate through a sliding rail, and the experimentalsection and a contraction section are in inserting fit through an inserting ring and a butting ring; a pressure balance gap is reserved between the experimental section and a diffusion section; the top, adjacent to the inserting ring, of the upper cover and the top, adjacent to the butting joint, of the contraction section are each provided with an electromagnet mechanism, and the two electromagnet mechanisms are arranged in a directly-facing mode, are matched with each other, and can output homopolar repulsion or heteropole attraction electromagnetic force; four gas collecting plates are arranged on the periphery of a hole in the gas inlet end of the diffusion section, the gas collecting plates located at the top, the front end and the rear end of the hole are connected with the hole inthe gas inlet end of the diffusion section through hinges, the gas collecting plate located at the bottom end of the hole is fixedly connected, and the four gas collecting plates form a complete gas collecting hood when being in a spliced mode; and a portal crane is erected above the experimental section, a lifting ring is mounted at the top of the upper cover of the experimental section, and theupper cover is hoisted and transferred through the portal crane.