The invention discloses a method for acquiring a machining error based on tool path data. The method comprises the following steps that tool path data output by a CAD/CAM software system are acquired, and the tool path data are preprocessed, so that cutting track data involved in cutting are acquired; regarding the cutting track data, chord errors of cutter location points are calculated through the three-point circle method, the chord errors of all the cutter location points are averaged, and a result is amplified by 40% to 60%, so that the machining error of a tool path track is obtained. According to the method for acquiring the machining error based on tool path data, the technical bottle neck facing optimizing process of the tool path data can be broken, a reasonable machining error is automatically calculated, and an important reference basis is provided for solving the problem of the tool path data output by an existing CAD/CAM software system, including repeated points, sharp points, point position information distribution nonuniformity and the like and the problem that the quality of the tool path track is severely influenced due to the fact that technical levels of numerical control programming personnel are various.