Objective To analyze the target volume margins and positioning errors in the radiotherapy for nasopharyngeal carcinoma(NPC)using the cone-beam computed tomography(CBCT)of Halcyon linear accelerator for providing a reference for the margin from clinical target volume to planning target volume(CTV-to-PTV margin)in the radiotherapy for NPC using Halcyon linear accelerator,hence improving treatment precision and effectiveness.Methods A total of 117 NPC patients who received volumetric modulated arc therapy using Halcyon linear accelerator from May 2020 to June 2022 in Jinshazhou Hospital of Guangzhou University of Chinese Medicine were enrolled.The 3861 CBCT images collected from the patients were matched with the CT images to obtain the correction values of the treatment couch in lateral(Lat),longitudinal(Lng)and vertical(Vrt)directions for positioning error analysis.The CTV-to-PTV margin was obtained by the equation(margin =2.5∑+0.7δ).Results The positioning errors in the radiotherapy for NPC using Halcyon linear accelerator were 0.10(0.00,0.10)cm,0.10(0.00,0.20)cm and 0.20(0.10,0.30)cm in Lat,Lng and Vrt directions,respectively.The CTV-to-PTV margins in Lat,Lng and Vrt directions were 0.12,0.12 and 0.09 cm,respectively.Conclusion Low positioning errors can be achieved for NPC patients undergoing image-guided treatment using Halcyon linear accelerator.