A 2-m-maglitude free-piston-driven high-enthalpy shock tunnel comprises a high-pressure gas storage chamber, a piston launching mechanism, a piston, a compression tube, a piston stop mechanism, a maincapsule mechanism, a shock wave tube, a small capsule mechanism, a spray tube, a test segment, a track and a support system. The high-pressure gas storage chamber is arranged at the upstream of the piston launching mechanism and stores high-pressure air. After being launched through the piston launching mechanism, the piston may move to the downstream of the compression tube at increased speed; when the piston arrives at the tail end of the compression tube, most energy is transmitted to helium-argon mixed light gas, and high-temperature high-pressure gas is generated; at this moment, a membrane of the main capsule mechanism breaks, incoming shock wave is generated and passes through the shove wave tube until its tail end, the shoe wave may be reflected, and high-temperature high-pressuregas is generated to cause breakage of a membrane of the small capsule mechanism. The high-temperature high-pressure test gas passes through the spray pipe to the test segment, and free stream conditions required are acquired.