A method for analyzing an overcutting defect of a machining process comprises steps as following. A machining code is executed to generate a cutting face, wherein the cutting face comprises a plurality of machining paths. A specified machining path is defined from the plurality of machining paths and a specified node is set on the specified machining path. A sectional plane passing through the specified node is calculated. A plurality of intersection points between the sectional plane and the other machining paths which are different from the specified machining path are obtained. A first adjacent intersection point a second adjacent intersection point are specified from the intersection points. A connection line located between the first adjacent intersection point and the second adjacent intersection point is obtained. A distance between the specified node and connection line is calculate and the distance is defined as an overcutting amount of the specified node.