Objective:To analyze the influencing factors for efficacy of microvascular decompression (MVD) in primary trigeminal neuralgia (PTN).Methods:A retrospective study was performed. Clinical data of 178 patients with PTN underwent MVD at Department of Neurosurgery, Affiliated Hospital Affiliated to Nantong University from January 2018 to April 2022 were collected. Efficacy was evaluated according to Brisman's criteria. Differences of MVD efficacy in patients with different clinical characteristics or different neurovascular characteristics were compared. Multivariate Logistic regression was used to analyze the independent influencing factors for MVD efficacy.Results:All patients were followed up for about 2 years; at the last follow-up, 164 patients (92.13%) had good postoperative efficacy (130 were cured, 28 were obvious improved, and 6 were improved); 14 patients (7.87%) had poor postoperative efficacy (10 were ineffective and 4 were relapsed). No significant difference in surgical efficacy was noted among patients with different gender, age, left/right lateral pain, disease courses or pain degrees ( P>0.05). Patients with different contact degrees between the trigeminal nerve and blood vessels, different distances between the trigeminal nerve and blood vessels, and different curvature degrees of the posterior trigeminal nerve had significantly different surgical efficacy ( P<0.05). Multivariate Logistic regression indicated that contact degrees between the trigeminal nerve and blood vessels ( OR=0.233, 95% CI: 0.080-0.675, P=0.007), distances between the trigeminal nerve and blood vessels ( OR=6.991, 95% CI: 3.261-14.984, P=0.000), and curvature degrees of the posterior trigeminal nerve ( OR=0.351, 95% CI: 0.158-0.776, P<0.001) were independent influencing factors for postoperative outcomes. Conclusion:The postoperative efficacy is good in patients with slight contact between the trigeminal nerve and blood vessels, with distance between the trigeminal nerve and blood vessels greater than 1×time median width of the trigeminal nerve (WTN), or with hypotenuse height of the arced trigeminal nerve less than 1/2 WTN.