The invention relates to the technical field of computer simulation, and discloses a method for judging thickness of a DEFORM-3D simulation turning surface grain refinement layer. Measurement is conducted on the thickness of the turning surface grain refinement layer by means of combination of a function that the grain size of materials can be measured through DEFORM-3D software and a C language judgment program according to the defect that on the condition of 3D turning simulation, DEFORM can not measure the thickness of the turning surface grain refinement layer. The method comprises the main steps of establishment and pretreatment of a cutting model, imitation of the cutting model, measurement of the original grain size of a matrix, dotting on the cutting surface from outside to inside, application of the C language judgment program, obtaining of variation boundary point values of the cutting surface grain refinement layer, connecting and measuring of obtained point values and the like. According to the method for judging the thickness of the DEFORM-3D simulation turning surface grain refinement layer, the thickness of the cutting surface grain refinement layer can be obtained more accurately, and the method is easier to operate and has better maneuverability.