Disclosed are a long-effect desert expansion inhibitor and a long-effect desert expansion inhibiting method. The inhibitor comprises a high-molecular composite material capable of cohering grains of sand and inhibiting sand drift, and a protective film material sprayed onto the surface of the high-molecular composite material to avoid fast degradation of the high-molecular composite material. The high-molecular composite material is prepared into a solution, and is then uniformly sprayed onto the surface of the desert, so that the solution can be naturally permeated into 10-30 cm sand of the surface layer; then, a suspension prepared from the protective film material is uniformly sprayed onto the treated desert surface. The degradation of the organic polymers can be inhibited, the effect period is prolonged, the degradation speed of the high-molecular compound is reduced by 20% or more, and the duration of efficacy of the inhibitor is prolonged by 30% or more, so as to achieve the purpose of long-effect sand fixation. The method is environmentally friendly and simple in operation, and has higher application value, and the desert soil leveling and stirring are not needed.