Abstract: The high-speed ion emits from the ion source during the ion beam processing impacts the optical mirror surface, thermal energy deposited inside the mirror which comes from kinetic energy and radiation of filament, makes the mirror temperature rise sharply. When the temperature of the mirror rises sharply, it could make cement of flexible components change irreversibly and nonlinearly, and the actual machining position is not the ideal position due to expansion, so it is necessary to suppress the thermal effect. A method of machining path planning and heat conduction enhancement was proposed to control the temperature of the mirror. For a primary mirror of 600 mm260 mm, research and finite element analysis were carried out for ion beam processing with different processing paths before and after heat conduction enhancement, which shows that the path selection and heat conduction enhancement have serious effects to the mirror. Before heat conduction enhancement, the maximum temperature of the mirror was 35.8 ℃, PV=/5 when horizontal grid-shape machining path was used, and the maximum temperature of the mirror was 52 ℃, PV=/10 when vertical grid-shaped machining path was used. After heat conduction enhancement, the temperature of mirror about all machining path declined, the maximum temperature of the mirror was 28.2 ℃, PV=/20, when horizontal grid-shape machining path was used and increasing the heat conduction path, the maximum temperature of the mirror was 52 ℃, PV=/10, when vertical grid-shaped machining path was used. By contrast, the method of horizontal grid-shape machining path was used and the heat conduction path was increased finally. The optimal path was tested experimentally. The results agree with the simulational result，and it shows that optimizing the processing path and enhancing heat conduction measures can suppress the thermal effect of ion beam processing. This research provides theoretical basis for the thermal effects suppression of ion beam processing.