Objective:To investigate the effect of the average diameter of regional lymph node on tumor recurrence after operation of pancreatic head adenocarcinoma without lymph node metastasis.Methods:Clinical data of 49 patients with pancreatic head adenocarcinoma admitted to the 909th Hospital of Joint Logistic Support Force from January 2017 to June 2019 were retrospectively analyzed. The receiver operating characteristic (ROC) curve was used to analyze the average regional lymph node diameter for predicting the optimal threshold of tumor recurrence. The relationship between the average diameter of regional lymph nodes, recurrence and clinicopathological features were analyzed. The influencing factors of tumor recurrence 3 years after surgery were analyzed by logistic regression.Results:All 49 patients with pancreatic head adenocarcinoma were divided into a relapse group ( n=29) and a no-recurrence group ( n=20) based on whether the tumor recurred or not, and the recurrence rate was 59.18%. ROC curve analysis showed that the best threshold of average regional lymph node diameter for predicting tumor recurrence was 0.635 cm, the area under the curve was 0.82, the sensitivity was 0.69, and the specificity was 0.85. The average diameter of regional lymph nodes increased in patients with tumor diameter ≥2 cm ( t=-2.12, P=0.040), tumor with moderate and poorly differentiation ( t=-2.24, P=0.013), vascular invasion ( t=-3.47, P=0.001), nerve invasion ( t=-3.75, P<0.001), capsular invasion ( t=-4.25, P<0.001), and tumor recurrence ( t=-4.42, P<0.001). Univariate analysis showed that tumor diameter ( χ2=5.98, P=0.015), tumor stage ( χ2=3.88, P=0.049), tumor differentiation ( χ2=5.98, P=0.015), vascular invasion ( χ2=3.84, P=0.050), capsular invasion ( χ2=5.79, P=0.016), average lymph node diameter ( χ2=15.61, P<0.001), and postoperative chemotherapy ( χ2=3.89, P=0.049) were all related to whether the tumor recurred or not in patients with pancreatic head adenocarcinoma 3 years after surgery. Multivariate analysis results showed that tumor diameter ≥2 cm ( OR=2.72, 95% CI: 1.46-11.28, P=0.016), tumor with moderate and poorly differentiation ( OR=2.22, 95% CI: 1.23-6.53, P=0.020), capsular invasion ( OR=2.30, 95% CI: 2.19-8.91, P=0.017), and average lymph node diameter ≥0.635 cm ( OR=7.93, 95% CI: 1.25-50.31, P=0.002) were all independent influencing factors for tumor recurrence in pancreatic head adenocarcinoma patients 3 years after surgery. Conclusion:In patients with pancreatic head adenocarcinoma without lymph node metastasis, tumor diameter ≥2 cm, tumor with moderate and poorly differentiation, capsular invasion and average lymph node diameter ≥0.635 cm are independent risk factors for postoperative tumor recurrence. Patients with the average diameter of regional lymph nodes ≥0.635 cm increase the possibility of tumor recurrence after surgery, which can be used as the basis for postoperative evaluation and has certain clinical application value.