Objective Clinical application of diffusion-weighted imaging (DWI) in nasopharyngeal carcinoma metastatic lymph node radiotherapy in the treatment process and by monitoring the apparent diffusion coefficient (ADC) to evaluate changes in the value of radiotherapy in patients with DWI. Methods Select the hospital after surgery and pathology confirmed 60 cases of nasopharyngeal carcinoma patients were studied, and the use of radiotherapy. Respectively, one day before the first chemotherapy, the second one days before chemotherapy, one day before the first radiotherapy, radiotherapy day and the 15th day of the 30th day of radiotherapy and one month after the end of treatment using MRI and DWI checks. Results (1) Before treatment, the mean ADC value of lymph node (0.792±0.019)×10-3mm2/s ADC values were significantly lower than normal tongue (1.387±0.035)×10-3mm2/s, P <0.05; (2) with the treatment progresses, patients with metastatic lymph nodes attendant rising ADC value, but during the first 1 to 15 times the most significant increase in radiation; (3) after treatment, the residual lymph nodes in patients with average ADC value (1.399±0.079)×10-3mm2/s was significantly higher than before treatment, P<0.05; but after treatment compared with normal tongue ADC value, P>0.05. Conclusion Through the use of DWI and MRI monitoring of metastatic lymph nodes in patients with nasopharyngeal carcinoma radiotherapy ADC value change during treatment, which can effectively evaluate the clinical efficacy, which provides a reference for the clinical treatment of patients rationalization.