The invention relates to a method of reducing deformation of a milled plastic material. The method is characterized by comprising the following steps: determining a milling rule of the plastic material through a single factor milling test of milling key parameters (milling speed, radial knifing and feed engagement); then carrying out an orthogonal milling test to determine the optimum milling keycutting parameters; carrying out a single factor milling test on milling radial feeding number of times of the plastic material to determine a reasonable radial feeding number of times of the plasticmaterial; and carrying out a milling processing test on the plastic material based on the optimum key cutting parameters and the reasonable radial feeding number of times to finally determine the optimum radial feeding number of times so as to achieve a purpose of reducing deformation of the milled plastic material. The method provided by the invention is simple in flow and high in operability anduniversal applicability, and can guarantee a relatively high surface quality on the premise of reducing deformation of a plastic material workpiece.