Objective To analyse and medium-term nasopharyngeal carcinoma radiotherapy follow-up the application value of magnetic resonance diffusion weighted imaging. Methods Our hospital in 100 cases of nasopharyngeal carcinoma radiotherapy patients as the research object, according to the different follow-up time will be divided into two groups, one group is the follow-up review time within 6 months after the treatment, a total of 42 cases, another group is the follow-up review between 6 months to a year after the treatment, a total of 58 cases. Two groups of patients and according to the tumor residual or recurrence of each within the group are divided into residual group (5 cases) and non residual group (37 cases), recurrent group (7 cases) and non recurrence group (51 cases), respectively in patients with each line of conventional MRI scans and magnetic resonance diffusion weighted imaging, observation of the imaging appearances of different groups of patients, and the groups of patients with lesion location and dilatory muscle of the apparent diffusion coefficient (ADC) is measured and compared. Results All patients were measured the dilatory muscle of ADC values, is the average of (1.63±0.21) ×10-3 mm2 /s. Distance radiotherapy within 6 months of 42 cases, 5 cases of tumor patients with residual ADC values (1.11±0.17)×10-3mm2 /s., 38 cases of patients with tumor residue, ADC values (1.88±0.23)×10-3mm2 /s. Distance radiation more than six months in 58 cases, 7 cases of patients with recurrence of ADC value is (0.81±0.08) ×10-3 mm2 /s., 51 cases of patients with recurrence of ADC value is (1.90±0.23) ×10-3mm2 /s. Residual tumor and recurrence in patients with ADC values were significantly lower than the dilatory muscle readings, without residue and is significantly higher than patients without recurrence dilatory muscle and ADC values in patients with tumor recurrence, more have statistical significance (P<0.05). Conclusion Magnetic resonance diffusion weighted imaging can changes after radiotherapy in patients with nasopharyngeal carcinoma lesions for effective display, provide a cellular level of qualitative and quantitative information, and the sensitivity of detection is higher, is helpful for the patients after radiotherapy of tumor residual prediction and diagnosis, recurrence, and so on and so forth, worthy of clinical popularization and application.