Abstract: Thermal error is a key factor affecting the machining accuracy of precision CNC machine tools. To effectively suppress machining errors caused by thermal deformation, a thermal error modeling and real-time compensation technology based on a programmable logic controller (PLC) was investigated. Firstly, a multi-channel temperature measurement system was established to monitor the temperature field at key structural points of a horizontal machining center in real time. Secondly, using the spindle rotation error analyzer and combining with the multi-point measurement method, the coupling influence of environmental temperature fluctuations and internal heat sources such as the spindle and the lead screw on the thermal error of the machine tool is quantified. Thirdly, based on the measured data, a highly accurate thermal error prediction model was established through multiple regression analysis. Finally, with the PLC as the core controller, combined with the thermal sensor and the analog quantity acquisition module, an online thermal error real-time compensation system was designed and implemented. The system drives the model calculation based on real-time temperature data and dynamically corrects the machine tool coordinates. The test results show that after applying this compensation system, the thermal errors of the machine tool's spindle and the Z-axis lead screw have been effectively controlled within 8 μm, significantly improving the processing accuracy. This verifies the effectiveness and engineering practicability of the proposed method.