Abstract： Objective To analyze the effect of clinical temporomandibular joint (TMJ) functional training for prevention of trismus in nasopharyngeal carcinoma (NPC) patients treated with radiotherapy.Methods According to the performance of patients clinical TMJ functional training, 43 NPC patients treated with three-dimensional conformal radiation therapy (3DCRT) and 82 NPC patients treated with general twodimensional radiation therapy were assigned respectively to the study group and the contrast group. The clinical TMJ functional training on patients of the study group was performed regularly and intensively under good guidance and supervision from the beginning of radiotherapy. The clinical TMJ functional training on patients of the contrast group was performed without such strict supervison after the first guidance. The size of the distance was measured between the incisors of the patients of the study group and the contrast group before radiotherapy and the final follow-up within two years after radiotherapy. Results The reduction of the distance between the incisors were [(0.64±0.59) cm] in the study group of 3DCRT in contrast to the [(0.81±0.64) cm] in the contrast group (P ＞0.05). The incidence of trismus was 8.1% in the study group of 3DCRT in contrast to the 21.1% in the contrast group (P ＞0.05); The reduction of the distance between the incisors were [(0.72±0.65) cm] in the study group of general two-dimensional radiotherapy in contrast to the [(1.64±0.73) cm] in the contrast group (P ＜0.01). The incidence of trismus was 19.0% in the study group of general two-dimensional radiotherapy in contrast to the 47.5% in the contrast group (P ＜0.01). Conclusion TMJ Functional training method is the good method that can lower the severity and the incidence of trismus in NPC patients treated with radiotherapy. It is more evident and more important for patients with general twodimensional radiotherapy.