Objective:To compare the dosimetric differences of different intensity-modulated radiation therapy (IMRT) plans for nasopharyngeal carcinoma (NPC). Methods: 5-, 7- and 9-ifelds of IMRT plans in 16 NPC patients were respectively designed and synchronous dimention technology was applied to compare the dosimetric differences in target areas and involved organs. Results:The recovery rate in target area was 95% while the plan was evidently worse in 5-ifeld than in 7- and 9-ifelds (P<0.05). Whereas the maximum dosage (Dmax), mean dosage (Dmean) and minimum dosage (Dmin) were similar between 7- and 9-ifelds (P>0.05), which were obviously lower in 5-ifeld, and the differences were both signiifcant (P<0.05). In addition, the conformity and homogeneity indexes in target area had no signiifcant difference between 7- and 9-ifelds, but were markedly better than in 5-ifeld (P<0.05). Indexes in each involved organs were the lowest in 5-ifeld than in other ifelds (P<0.05), but were similar between 7- and 9-ifelds (P>0.05), which were all lower than tolerant dosage. As for BODY, there were significant differences in V10~V20between 5-ifeld and other ifelds (P<0.05), but were similar in V25~V30(P>0.05). However, 7- and 9-ifelds were similar in V10~V20 (P>0.05). Conclusion:7-field IMRT plan is the optimal one for NPC on both clinical dosimetric requirements and ifeld-establishment principles.