The invention provides an anti-pilling agent for a wool fabric. The anti-pilling agent consists of the following materials in parts by mass: 15-20 parts of ethyl acrylate, 15-20 parts of polyoxyethylene octyl phenyl alcohol, 10-15 parts of zinc nitrate, 5-8 parts of stearic acid, 5-8 parts of sodium sulfate, 2-4 parts of n-butyl alcohol, 2-4 parts of potassium tartrate, 1-3 parts of chitosan, 2-4 parts of sodium dihydrogen phosphate, 70-80 parts of ethyl alcohol and 320-360 parts of water. The invention also provides a preparation method of the anti-pilling agent. By virtue of the anti-pilling agent, the anti-pilling grade of the wool fabric can be enhanced by over two levels and the hydrophilicity can be kept the same fundamentally.