Objective To investigate the diagnostic efficacy of ultrasonography in the diagnosis of extraglandular invasion of papillary thyroid microcarcinoma (PTMC) and its related influencing factors, in order to provide a basis for clinical diagnosis. Methods The clinical data of 156 patients (200 nodules) with PTMC admitted to The Fifth Hospital of Harbin City from January 2020 to February 2022 were retrospectively analyzed, all the patients were examined by ultrasonography before operation, postoperative pathological examination results were as the gold standard, the results of preoperative ultrasonography in the diagnosis of extraglandular invasion of PTMC and its diagnostic efficacy were analyzed, the accuracy of ultrasonography in the diagnosis of extraglandular invasion of PTMC was analyzed by single factor analysis, and the factors with statistical significance were analyzed by multivariate Logistic regression analysis. Results Among 156 cases (200 nodules) with PTMC, 106 nodules with extraglandular invasion were confirmed by pathological examination, 94 nodules without extraglandular invasion, the results of ultrasonic diagnosis showed that 88 nodules were in contact with the thyroid capsule, and 112 nodules were not in close contact with the capsule, among which 76 were true positive (true positive group) and 30 were false negative (false negative group); the sensitivity, specificity, accuracy, positive predictive value and negative predictive value of ultrasonography in the diagnosis of extraglandular invasion of nodules with diameter >5 mm were significantly higher than those with nodules diameter ≤?5 mm. The results of single factor analysis showed that the proportion of nodule with diameter ≤?5 mm, microcalcification, nodule not adjacent to the trachea and unilateral lobe lesions in the false negative group were significantly higher than those in the true positive group (all P<0.05); multivariate Logistic regression analysis showed that the the diameter ≤?5 mm, microcalcification, unilateral lobar lesion and nodule not adjacent to the trachea were all independent risk factors for false negative results of PTMC extraducular invasion by ultrasonography (OR=3.415, 3.884, 4.121, 2.556, all P<0.05）. Conclusion For PTMC, ultrasonography is of high diagnostic efficacy for lesions with nodule diameter >5 mm, the diameter ≤?5 mm, microcalcification, unilateral lobar lesion and not adjacent to the trachea were independent risk factors for the accuracy of ultrasonic diagnosis of extraglandular invasion of PTMC, so when the above risk factors are present, pathological examination should be taken to further confirm the diagnosis and improve the accuracy