Abstract: Objective To evaluate the primary gross tumor volume(GTV)on prognosis in patients with local advanced nasopharyngeal carcinoma. Methods The clinical data and follow-up data of 310 patients with nasopharyngeal carcinoma in Ⅲ to IVA/B phase undergoing chemoradiotherapy were retrospectively analyzed. The optimized critical value of GTV was confirmed as 34.1 mL by Receiver Operating Characteristic(ROC)curve analysis. A total of 106 cases with GTV>34.1 mL were included in the experimental group. Propensity matched study method was used to adjust for age, gender, Karnofsky Performance Status(KPS), tumor stage, node stage, and clinical stage. At last, a well-balanced cohort(106 cases who had GTV of less or equaling to 34.1 mL)was created by 1∶1 matching in the control group. Survival rate was calculated using Kaplan-Meier method, and prognostic factors were analyzed using Cox regression model. The primary end-point was loco-regional relapse-free survival rate(LRRFS), secondary end-points were overall survival(OS)and distant metastasis-free survival(DMFS). Results The experimental group had lower 4-year LRRFS and OS when compared to the control group(80.2% versus 92.5%, 77.4% versus 84.0%, P=0.008, 0.043). The 4-year DMFS of the experimental group and the control group were 68.9% and 74.5%, respectively, but no significant difference was found(P=0.273). Cox regression model showed that GTV >34.1 mL was an adverse influencing factor of LRRFS and OS. Conclusion GTV>34.1 mL is an adverse influencing - factor for loco-regional progress and death in local advanced nasopharyngeal carcinoma. It is necessary to increase the treatment intensity in order to obtain better clinical efficacy.