The invention belongs to the technical field of pesticides, and particularly relates to a plant growth regulator and an application method thereof. Effective components of the plant growth regulator comprise alternaria tenuissima activated protein and any one selected from diethyl aminoethyl hexanoate, zeatin and compound sodium nitrophenolate. According to the plant growth regulator, and wettablepowder, water dispersible granule, suspension and water aqua thereof, the alternaria tenuissima activated protein and any one selected from diethyl aminoethyl hexanoate, zeatin and compound sodium nitrophenolate are mixed with each other to be used as the effective components, and the action mechanisms are different; after compounding, a synergistic effect is achieved under a defined usage concentration and usage method according to various crops such as rice, corns, wheat, peanuts, cotton, vegetables, tobaccos, fruit trees, gardens, flowers and the like, and the yield and the income are increased; an obvious weight-increasing effect is achieved for fruits of the fruit trees, and the chlorophyll content of plants is effectively improved; and moreover greenness preservation and an anti-aging effect are achieved, the sugar content is improved, growth of the crops is promoted, and quality of the fruits is effectively improved.