Abstract Background There has been no ideal treatment for freezing-phase frozen shoulder to rapidly relieve pain and improve joint mobility. No any other team directly compared the effectiveness of combination of arthroscopic release and corticosteroid hydrodilatation with corticosteroid hydrodilatation only in treatment of freezing-phase frozen shoulder. Methods Seventy-two patients with freezing-phase frozen shoulder were randomly assigned to combined arthroscopic release with corticosteroid hydrodilatation (group A) or corticosteroid hydrodilatation only (group B). Clinical states were examined at baseline and periodically (Weeks 1, 4, 12, 24 and 1 year) after intervention by passive ROM; visual analog scale (VAS); UCLA and Disabilities of the Arm, Shoulder, and Hand (DASH) score. Results The passive ROM, VAS, UCLA and DASH scores always improved along the time points (all p 0.01), the differences between group A and group B were all lower than minimal clinically important difference (MCID). At Week 12, the UCLA sores and DASH scores were 26.8 ± 3.8, 14.2 ± 2.0 in group A versus 22.3 ± 3.4, 22.5 ± 3.1 in group B (all p