To view and evaluate the prognosis factors in patients with nasopharyngeal carcinoma (NPC) treated with intensity modulated radiation therapy using nomogram and decision curve analysis (DCA).Based on a primary cohort comprising consecutive patients with newly confirmed NPC (n = 1140) treated between January 2014 and December 2015, we identified independent prognostic factors of overall survival (OS) to establish a nomogram. The model was assessed by bootstrap internal validation and external validation in an independent validation cohort of 460 patients treated between January 2013 and December 2013. The predictive accuracy and discriminative ability were measured by calibration curve, concordance index (C-index) and risk-group stratification. The clinical usefulness was assessed by DCA.The nomogram incorporated T-stage, N-stage, age, concurrent chemotherapy and primary tumour volume (PTV). The calibration curve presented good agreement for between the nomogram-predicted OS and the actual measured survival probability in both the primary and validation cohorts. The model showed good discrimination with a C-index of 0.741 in the primary cohort and 0.762 in the validation cohort. The survival curves of different risk-groups were separated clearly. Decision curve analysis demonstrated that the nomogram provided a higher net benefit (NB) across a wider reasonable range of threshold probabilities for predicting OS.This study presents a predictive nomogram model with accurate prediction and independent discrimination ability compared with combination of T-stage and N-stage. The results of DCA supported the point that PTV can help improve the prognostic ability of T-stage and should be added to the TNM staging system.