Objective To compare the therapeutic effects in treating patients in early stage of primary frozen shoulder undergoing ultrasound-guided hydrodistension under different capacity. Methods 120 patients with PFS in early stage who received ultrasound-guided hydrodistension in our clinic from June 2022 to October 2023 were randomly divided into low capacity group (group L), median capacity group (group M) and high capacity group (group H)，40 cases in each group. The numerical rating scales (NRS) pain scores, active range of motion (AROM), activity of daily living (ADL) scores were recorded before and 1 mo, 3 mo and 6 mo after the treatments. The NRS scores for the most severe pain during the hydrodistension procedure, the NRS scores for treatment satisfaction and the use of oral analgesics and patient satisfaction with recovery at different time points after treatment were also recorded. Results 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 ultrasound-guided hydrodistension (P＞0.05). The three groups also showed no ignificant differences in the use of oral analgesics and patient satisfaction with recovery at different time points after treatment (P＞0.05). However, group H showed higher NRS scores for the most severe pain during the hydrodistension procedure than the other two groups (P＜0.05). Meanwhile, the NRS scores for treatment satisfaction were lower in group H than that in group L and group M (P＜0.05). Conclusion There is no significant difference in the therapeutic effects in treating patients in early stage of primary frozen shoulder undergoing ultrasound-guided hydrodistension under different capacity. However, hydrodistension with high capacity could cause more severe pain and thus decrease the satisfaction of the treatments.