Objective To compare the therapeutic effects in patients with primary frozen shoulder (PFS) undergoing manipulation under anesthesia (MUA) at different operation time. Methods We performed a retrospective review of patients with a primary frozen shoulder treated by MUA from June 2019 to June 2021. According to the duration of presenting symptoms, they were divided into four groups: group A (within 3 months), group B (3 to 6 months), group C (6 to 9 months) and group D (9 to 12 months). The numerical rating scales (NRS) pain scores, active range of motion (AROM), activity of daily living (ADL) scores and satisfaction with recovery were recorded before surgery and 1 mo, 3 mo and 6 mo after surgery. Meanwhile, the use of analgesics and the incidence of recurrent adhesion within 12 months after surgery were also recorded. Results A total of 129 patients were selected for the statistical analysis, including 33 in group A, 35 in group B, 32 in group C, and 29 in group D. Compared with basal, NRS, AROM and ADL scores improved significantly (P＜0.05). The results of ANOVA between groups showed that there were no significant differences in NRS, AROM and ADL scores at each time point after surgery (P＞0.05). Compared with group D, the use of analgesics in Group A within 1 month after surgery was significantly increased (P＜0.05). Meanwhile, patient satisfaction with recovery in group D within 1 month after surgery was significantly higher than that in Group A (P＜0.05). There were no significant differences in the incidence of recurrent adhesion between the four groups (P＞0.05). Conclusion There is no significant difference in the therapeutic effects in patients with primary frozen shoulder undergoing manipulation under anesthesia at different operation time. Therefore, early intervention is more recommended for patients with primary frozen shoulder to shorten disease duration and accelerate the recovery of shoulder function.