The invention belongs to the field of biodegradable high-polymer materials and particularly relates to a mechanically-applied ultrathin, ultrahigh-strength and ultra-transparent fully-biodegradable mulching film. The mechanically-applied ultrathin, ultrahigh-strength and ultra-transparent fully-biodegradable mulching film is composed of fully-biodegradable resin, strengthening, toughening and transparent agent and processing agent, wherein the strengthening, toughening and transparent agent can solve the problem that ultrathin mulching films are poor in mechanical strength, easy to break and difficult in mechanical application; the processing agent solves the problem of opening difficulty and low efficiency during processing of the ultrathin mulching films; by optimizing the variety of the fully-biodegradable resin and combining with functional additives, the ultrathin, ultrahigh-strength and ultra-transparent fully-biodegradable mulching film with a thickness of 4-6 mu m is developed, and meanwhile, the mechanically-applied ultrathin, ultrahigh-strength and ultra-transparent fully-biodegradable mulching film is high in transparency, reaches a light transmittance lower than 91%, a haze degree lower than 12% and a high mechanical tensile strength higher than 25 MPa, thereby meeting the requirements of common mulch applicators on mulching film strength. The mechanically-applied ultrathin, ultrahigh-strength and ultra-transparent fully-biodegradable mulching film meets the PE (polyethylene) mulch film mechanical application standards on tensile strength, breaking elongation and right-angled tearing strength as well as exceeds or meets the GB 13735-92 specifications on physical and mechanical properties.