Objective　To investigate the effect and mechanism of yin deficiency constitution on radio sensitivity of nasopharyngeal carcinoma.　Methods　150 patients with nasopharyngeal carcinoma who were treated in the traditional  Chinese medicine department of Nanfang Hospital were selected for grouping and constitutional identification. Methylation-specific PCR (MSP) was used to detect the methylation status of CpG islands in the promoter region of tumor suppressor gene (RASSF1A, TP53, PTEN) and real-time fluorescence quantitative (qPCR) detection of its expression.　Results　According to the TCM Constitution Questionnaire and the four diagnoses of TCM, the constitution of the patients was identified. Among the 112 patients with radio sensitivity, 20 were yin deficiency constitution, accounting for 17.86% of the total number. Among the 38 patients who were relapsed (radiation resistance), 28 were yin deficiency constitution, accounting for 73.68% of the total number. Compared with other constitution patients, the proportion of methylation of tumor suppressor genes (RASSF1A, TP53, PTEN) in patients with yin deficiency constitution increased significantly, and gene expression was down-regulated.　Conclusions　Yin deficiency constitution is more likely to have radio resistance, and the inactivation of tumor suppressor gene caused by hypermethylation may be an intrinsic mechanism of radiation resistance in patients with yin deficiency constitution and nasopharyngeal carcinoma.