Mulching film is an important material in ecological restoration, such as desert control, saline alkali land improvement, and slope greening protection. At present, both solid and liquid mulching films are mainly made of man-made materials, which have a great impact on the ecological environment and are expensive. Naturally weathered red-bed soil mud films are being applied in the construction industry because of their advantages of environmental friendliness and low cost. However, at present, film formation needs to occur under pressure, in complex processes, which results in great application limitations, so it is difficult to popularize and apply these natural mud films to the field of ecological restoration. Therefore, exploring high-quality film formation under pressureless conditions is key for the application of naturally weathered red-bed soil mud films in the field of ecological restoration. To solve this problem, this paper takes naturally weathered red-bed soil, without additives; designs and carries out mud film-forming tests of naturally weathered red-bed soil and a comparison test with bentonite under pressureless conditions; tests the influence of mud particle gradation, viscosity and moisture content on the film-forming effect; optimizes the mud film-forming ratio; and further studies the thickness, water resistance, compression resistance. Acid and alkali resistances are tested and compared with international standards. The results show that the naturally weathered red-bed soil can form a mud film under pressureless conditions. The optimal (high-quality) film corresponds to a mud viscosity of 29.6-52.6 Pa·s, water content of 15-35%, and content of particles with particle sizes smaller than 1 mm of 75%-85%. Compared with international standards and bentonite, the naturally weathered red-bed soil mud film meets the ecological restoration standard, has a better water resistance, compression resistance, and acid and alkali resistances than bentonite mud film, and has the advantages of a wide distribution, low cost, simple sample preparation and wide application range. Therefore, weathered red-bed soil mud film is a film technology with obvious comparative advantages that can be introduced into the field of ecological restoration and has broad prospects.