Objectives Highly efficient diabetes management programs are needed for tackling diabetes in China. This study aimed to assess the effectiveness of a clinic-based intensified diabetes management model (C-IDM) in Mainland China. Research design and methods A 2-year clinic-based randomized controlled trial was conducted among patients with type 2 diabetes in Nanjing, China. The C-IDM intervention components comprised four domains (disease targeting management, express referral channel, expert visit, patients' self-management) and an integrated running system (disease control centers, general hospitals and local clinics). Control group participants received their usual care, while intervention participants received both the C-IDM package and the usual services. The primary outcome variable was change of hemoglobin A1c (HbA1c). Mixed-effects models were used to compute effect estimates and 95% CI with consideration of both individual and cluster-level confounders. Results Overall, 1095 of 1143 participants were assessed at study completion. The mean change in HbA1c was significantly greater in the intervention group than in the control group (mean difference (MD)=-0.57, 95% CI-0.79 to-0.36). Similar results were observed for change in body mass index (MD=-0.29, 95% CI-0.49 to-0.10). Participants in the intervention group were more likely to achieve normal HbA1c and body weight compared with their counterparts in control group after adjusting for potentially confounding variables (adjusted OR=1.94, 95% CI 1.35 to 2.81 and 1.79, 95% CI 1.13 to 2.85, respectively). Conclusions The C-IDM model is feasible and effective in large-scale management of patients with type 2 diabetes in China. It has public health implications for tackling the burden of diabetes in China. Trial registration number ChiCTR-IOR-15006019.