Objective To study the relationship between radioactive otitis media and changes in cross section area of tensor veli palatine (TVP) muscle after radiotherapy in patients with nasopharyngeal carcinoma. Methods Retrospectively analyze the clinical data of 36 patients with nasopharyngeal carcinoma who accepted radiotherapy in our hospital from January, 2007 to January, 2011. The cross section area (CSA) of TVP and medial pterygoid (MP) muscle of all the patients were measured before and after radiotherapy, meanwhile the incidence of SOM was surveyed after radiotherapy. Results Twenty-four cases (44 ears) developed post-irradiation SOM after the radiotherapy. STVP, SLTVP, SRTVP, SLTVPM, SRTVPM, SLTVPF, SRTVPF, SMP, SLMP and SRMP of all patients statistically decreased after radiotherapy (P<0.05). Ears with TVP atrophy had a high rate of incidence of SOM than ears without TVP atrophy (72.92% vs 37.50%, χ2=8.445, P=0.004). Conclusion The atrophy occurs to the CSA of TVP and MP of patients with nasopharyngeal carcinoma, which may result in post-irradiation SOM.