Purpose Idiopathic sudden sensorineural hearing loss is a clinical emergency with an increased incidence of occurrence in recent years. Hyperbaric oxygen has been widely used in the clinical treatment of sudden hearing loss. However, prognostic factors related to its curative effects are still not clear, which hinders its clinical application. The aim of this study was to investigate the efficacy and prognostic factors of hyperbaric oxygen therapy (HBOT) plus drug therapies in the treatment of sudden hearing loss. Method Patients with sudden hearing loss who were treated with hyperbaric oxygen from April to October 2017 were retrospectively included. Clinical information was collected, including pure-tone audiometry data before and after hyperbaric oxygen treatment, age, gender, hearing curve classification, concomitant symptoms, history of diseases (diabetes and hypertension), history of hormone therapy, start time of hyperbaric oxygen treatment, and total number of hyperbaric oxygen treatments. The prognostic factors were analyzed with univariate and multivariate analyses. Results Sixty-four patients with sudden hearing loss were enrolled, including 7 cases of low-frequency loss, 4 cases of high-frequency loss, 32 cases of flat loss, and 21 cases of complete hearing loss. After HBOT, there were 16 cases (25%) of complete recovery, 15 cases (23.43%) of partial recovery, 7 cases (10.93%) of slight improvement, and 26 cases (40.63%) of no improvement. The total effective rate was 59.37%. Twelve of 21 cases (57.14%) of complete hearing loss showed recovery. Multivariate logistic regression analysis showed that the start time of HBOT ≤ 7 days from disease onset was independently associated with hearing recovery ( OR = 27.763, 95% CI [4.209, 183.115], p = .001). Conclusion Combined HBOT can improve the hearing impairment of sudden hearing loss. The early HBOT showed the most promising therapeutic effects, especially among patients with complete hearing loss.