Craniomaxillofacial bone defects result in physical and psychological dual injuries making the promotion or acceleration of bone regeneration imperative. In this work, a fully biodegradable hydrogel is facilely prepared via thiol-ene "click" reactions under human physiological conditions using multifunctional poly(ethylene glycol) (PEG) derivatives as precursors. This hydrogel shows excellent biological compatibility, enough mechanical strength, a low swelling rate and an appropriate degradation rate. Rat bone marrow mesenchymal stem cells (rBMSCs) can survive and proliferate on/in the PEG hydrogel and differentiate into osteogenic cells. The PEG hydrogel can also effectively load rhBMP-2 through the above "click" reaction. Under the physical barrier of the chemically crosslinked hydrogel network, the spatiotemporal release of rhBMP-2 effectively promotes the proliferation and osteogenic differentiation of rBMSCs at a loading concentration of 1 μg ml-1. Finally, based on a rat calvarial critical-size defect model, the rhBMP-2 immobilized hydrogel loaded with rBMSCs basically accomplishes the repair and regeneration within 4 weeks featured by remarkably enhanced osteogenesis and angiogenesis. The click-based injectable bioactive PEG hydrogel developed in the present study is a new type of bone substitute with great expectations in future clinical applications.