The objective of this study is to investigate the risk factors of oral or facial herpes simplex virus (HSV-1) infection after primary trigeminal neuralgia (PTN). The clinical data of 33 PTN patients admitted by the same surgeon in the neurosurgery were retrospectively analyzed. Among the 33 patients, 26 patients underwent microvascular decompression (MVD), 6 patients who have not been found the clear offending vessels during the operation underwent partial sensory rhizotomy (PSR), and only one underwent adhesive band separation. Thirteen patients with postoperative oral and facial HSV-1 infection were selected as the herpes group, and the remaining 20 patients without postoperative oral and facial HSV-1 infection were selected as the non-herpes group. The differences between the two groups were compared by statistical analysis of factors such as gender, age, operation mode, operation time, and serum HSV-1 antibody titer value before surgery. Compared with the non-herpes group, there were no statistically significant differences in sex ratio (P = 0.930), age composition (P = 0.261), or disease profile (P = 0.226). Twenty-six patients underwent MVD operation, eight of whom were infected, and the difference between the two groups was statistically significant (P = 0.029). The operation time of the herpes group was 10-30 min, which was significantly longer than that of the non-herpes group. The difference in operation time between the two groups was statistically significant (P = 0.023). Serum HSV-1-IgM was negative (< 0.9 COI) in all patients before surgery, but the positive rate of HSV-1-IgG (>= 1.1 COI) was 97%, and the titer was greater than four times in 97% (32/33) of patients. The titer of IgG antibody in the herpes group was significantly lower than that in the non-herpes group, and the difference between the two groups was statistically significant (P = 0.017). The serum HSV-1-IgG in most of the PTN patients was positive. Latent HSV-1 in the trigeminal ganglion may be reactivate after PTN surgery to produce ipsilateral oral and facial herpes infection. The infection of HSV-1 reactivation after PTN surgery was positively correlated with the operation time but negatively correlated with the titer of HSV-1-IgG antibody before PTN surgery. The incidence of HSV-1 infection after PTN operation is related to different surgical procedures.