Abstract: Analyze the geometric errors of a five-axis linkage gantry milling machine, and combine the ideal position matrix and ideal motion matrix, position error matrix and motion error matrix of the machine tool topology and multi-body system theory. The laser interferometer is used to move the machine tool only along the three coordinate axes. Errors detection and identification of the roll angle errors; After compensation for the various geometric errors of the translational axis, use the Renishaw ballbar to be parallel to the direction of the three-coordinate axis to perform the C-rotation axis errors detection; when installing the ballbar, there is an offset along the Y axis, and the errors detection of the B axis is performed to identify the linear displacement errors and the angular displacement errors. Finally, 37 geometric error parameters of the five-axis linkage gantry milling machine are obtained, which lays the foundation for subsequent error compensation.