The invention belongs to the agriculture technical field, in particular to a cultivation method for preventing decayed fruits of a plain mulching film peanut; the cultivation method comprises the following steps: a ridge is formed on the field with the ridge height of 14cm to 15cm, the row spacing of 85cm to 90cm and the width of the ridge surface of 55cm to 60cm; two lines of sowing furrows are formed for seeding with the line distance of 35cm to 40cm; mulching films are covered; the mulching films are uncovered before large quantities of peanuts are deep into the soil and bear fruits; the method of the invention increases the evaporation area of the soil by increasing the height of the covered peanut ridge and carrying out manual film-uncovering in the formation stage of the yield of the peanuts, thus leading the water of the surface of the soil to evaporate smoothly and the amount of field evaporation to be larger than that when the mulching film is covered, guaranteeing the permeability of the soil of a peanut-bearing layer, reducing the decayed fruit rate of the peanuts effectively and improving the yield and the quality of the peanuts.