Abstract [Objective] To study the effect of different doses of recombinant human bone morphogenetic protein-2 (rhBMP-2) combined with absorbable collagen sponge (ACS) in repairing critical size bone defect (CSD) of rabbit radius and its dose-effect relationship. [Methods] 36 New Zealand white rabbits were randomly divided into 12 groups with 3 rabbits in each group according to the random number table method, and the experimental model of 15mm critical bone defect in the middle radius of one side of New Zealand white rabbits was made and divided into the following groups for treatment: Groups A~C and D~F respectively were 4 and 8 weeks experimental groups, each experimental group was divided into low dose experimental group (0.25mg RHBMP-2 +ACS, A/D group), medium dose experimental group (0.5 MgrhbMP-2 +ACS, B/E group) and high dose experimental group (2.5 MgrhbMP-2 +ACS, C/F group) according to the implanted dose of RHBMP-2; Ctr1a-ctr3a and Ctr1b-Ctr3b respectively were 4 and 8 weeks control groups, which were divided into empty sponge control group (ACS, Ctr1a/ Ctr1b), blank control group (Ctr2a/ Ctr2b) and bone graft control group (Ctr3a/ Ctr3b) according to treatment methods. 4 and 8 weeks after surgery, X-ray was used to observe the appearance of bone repair in each group. Micro-CT scan and 3D reconstruction were performed to observe the effect of bone repair in the defect area and quantitatively analyze the osteogenesis related indicators. Tissue sections were stained with HE to observe the maturation of new bone in each group. [Results]: The general observation, X-ray and Micro-CT showed that new bone was formed in the radius defect area in the three dose groups at 4 and 8 weeks postoperatively.In comparison, the high dose group had the best osteogenesis effect, followed by the medium dose group, and the low dose group had the worst osteogenesis effect, and the pairwise comparison between groups had statistical significance (P<0.05).The results of tissue section showed that the new bone maturity was best in the high-dose group at 4 and 8 weeks after operation, followed by the medium-dose group and the low-dose group.The effect of the empty sponge group was the same as that of the blank group, and no obvious bone growth was observed. [Conclusion]: rhBMP-2 can promote the repair of rabbit radius critical bone defect; In the range of 0.25mg-2.5mg, the effect of bone repair was positively correlated with the dose of rhBMP-2.