Abstract: This paper introduces a software compensation system for thermal error of CNC lathe spindle based on a PMAC multi-axis motion controller. Through secondary development of the PMAC multi-axis motion control card, the system can calculate the error compensation value based on the temperature value measured by the digital temperature sensor on the spindle and a pre-established thermal error model. The error compensation value is then applied to the tool path in real time via the PMAC card, thereby achieving real-time compensation for thermal errors and improving machining accuracy. Keywords: PMAC multi-axis motion controller, thermal error compensation, CNC lathe spindle. With the widespread application of CNC machine tools and precision machining, higher requirements have been placed on the machining accuracy of CNC machine tools. Error compensation technology can effectively improve the machining accuracy of CNC machine tools. Error compensation control, after obtaining the error model, reflects it in the actual machining process of the machine tool, causing the tool and workpiece to generate a certain relative motion in the machine tool's workspace along the opposite direction of the error, thereby achieving error compensation and improving the machining accuracy of the machine tool. Thermal error is the largest error source for CNC machine tools, accounting for approximately 50% of the total machine tool error. Therefore, reducing thermal error is crucial for improving the machining accuracy of machine tools. Thermal errors can be reduced through design improvements, temperature control, and error compensation. Error compensation is a simple and effective method that is gaining increasing attention. However, due to the closed nature of their structure, dedicated CNC systems make it difficult for researchers to perform secondary development and integrate thermal error compensation functions. This paper introduces a software compensation system based on a Programmable Multi-Axis Controller (PMAC). Experiments demonstrate that this software compensation system can achieve real-time thermal error compensation during machine tool processing, significantly improving machining accuracy. 1. PMAC Multi -Axis Controller PMAC is a high-performance servo motion controller launched by Delta TauData Systems in the United States. It is a multi-axis, multi-channel open motion controller based on an industrial PC and Windows operating system. The PMAC multi-axis motion controller can control 1-8 axes simultaneously, and can execute programs stored internally by the controller, as well as motion programs and PLC programs. It is also a real-time, multi-tasking computer that can automatically determine task priorities. For details, please click: Research on Thermal Error Compensation System for CNC Lathe Spindle Based on PMAC