The invention relates to an opened circulating Stirling engine comprising a hot-end cylinder, a hot-end piston, a regenerator, a cold-end cylinder and a cold-end piston. The regenerator is an one-way regenerator, the cold-end inlet and hot-end outlet of the one-way regenerator form a low-temperature medium channel, and the hot-end inlet and cold-end outlet form a high-temperature medium channel; the cold inlet of the cold-end cylinder is communicated with the air, and the cold outlet is communicated with the cold-end inlet of the one-way regenerator; the hot inlet of the hot-end cylinder is communicated with the hot-end outlet of the one-way regenerator, and the hot outlet is communicated with the hot-end inlet of the one-way regenerator; the cold-end outlet of the one-way regenerator is communicated with the air. The circulating medium adopts the one-way flowing manner, the heat exchanging manner is optimized, and the regenerating efficiency is improved; an absolute sealing device for a power piston and an expanding piston is omitted, the friction resistance is reduced greatly, and engine mechanical efficiency is improved; meanwhile, the medium is of the air, the operating pressure and temperature are low, expensive temperature-resistant material is omitted, cost is low, reliability is high, energy is saved, and environment is protected.