<p>Heavy-duty computer numerical control (CNC) machine tools have the characteristics of long motion stroke and large cutting load due to their large component size and large span. These characteristics will directly affect the machining accuracy of the machine tool. To improve the machining accuracy and overall performance of heavy-duty vertical lathes, a geometric error model is established using multi-body system theory and homogeneous coordinate transformation. Then, the geometric errors of machine tools are measured and analysed to obtain the change trend of the errors. To balance workload reduction and high compensation accuracy, key geometric errors influencing machining accuracy are identified through error sensitivity analysis. Finally, the internal relationship among tool path, numerical control (NC) instruction and tool trajectory is explored. The geometric error compensation principles and software compensation methods for three basic motions are also clarified. An error compensation calculation method based on reverse offset principle and Newton interpolation is proposed to correct NC instruction for achieving the effective geometric error compensation. Experimental results show that the proposed method has reduced the positioning errors, straightness errors and verticality error in the key geometric errors by more than 80%, 10% to 60% and 17.52% respectively. It demonstrates the significant effectiveness of the proposed method, and provides a successful case for the control of geometric errors and the improvement of machining accuracy in heavy-duty vertical lathes.</p>