Objective to investigate the value of ultrasound-guided fine needle aspiration cytology (FNAC) combined with BRAFV600E gene detection in preoperative diagnosis of thyroid micropapillary carcinoma (PTMC).Methods The preoperative diagnosis and treatment data of 126 cases of PTMC confirmed by surgery and pathology were retrospectively analyzed. FNAC and BRAFV600E gene mutation detection of fine needle suction extract were performed on all nodules.. The nodules were classified according to the maximum diameter of two-dimensional ultrasound ≤5 mm and 5-10 mm, and the FNAC results, genetic test diagnosis results, and postoperative pathology were compared and analyzed.Results the diagnostic accuracy of FNAC between the two groups ≤5mm and 5-10mm was 58.06% and 86.31%, and the accuracy of cytology in the 5-10mm group was significantly higher than that in the ≤5mm group, with statistical significance (P < 0.05). The mutation rates of fine needle aspiration BRAF V600E gene detection were 90.32% and 92.63%, with no statistical significance between the two groups (P > 0.05). The diagnostic accuracy of FNAC combined with BRAFV600E gene detection for ≤ 5 mm, 5 – 10 mm and overall groups was: 93.54%, 97.78%, and 96.82%, and the diagnostic accuracy of the combination of the two was significantly higher than that of FNAC, and the difference was statistically significant(P < 0.05). Some thyroid nodules were difficult to be diagnosed by FNAC（4/126 nodules were misdiagnosed as benign, 22/126 nodules were difficult to diagnose）, but the diagnostic accuracy was 84.61% after combined detection of BRAFV600E gene, and gene diagnosis technology played a good role in auxiliary diagnosis.ConclusionFNAC is greatly affected by the size of thyroid nodule. The smaller the nodule (≤5mm), the higher the proportion of missed diagnosis and misdiagnosis cases. The preoperative predictive value of FNAC combined with BRAFV600E gene test for PTMC is better than that of FNAC alone, which can significantly improve the diagnostic accuracy of PTMC. The combination of FNAC and BRAFV600E can significantly make up for the deficiency of FNAC alone in diagnosis, and has high clinical value especially for nodules with unclear FNAC nature.