Abstract: In order to solve the difficult issue about squareness error identification for linear axes in large gantry machine tools, the mapping relationship between the dynamic expressions of squareness errors and the volumetric positioning error of machine tool is built. Then, a laser interferometer based linear axes squareness error identification method is proposed. Experiments are conducted to compare the effect of the proposed method with the tradition measurement method by using marble square. Results show that the proposed method can obtain the squareness error more accurately and also can avoid the deficiencies, such as limitation of measurement range and easy to be influenced by operator during the measuring process. The proposed squareness error identification method can provide important directions for the accuracy adjustment and error compensation of linear axes in large gantry machine tools.