Amphiphilic block copolymer of poly(ethylene glycol) and polymer containing N'-Propargyl-N,N-dimethylacetamidines (PEG-b-PADS) was easily synthesized via the combination of reversible addition-fragmentation chain transfer polymerization (RAFT) and click chemistry. The structure of the copolymer was characterized by nuclear magnetic resonance (H-1 NMR) and attenuated total internal reflectance fourier transform infrared spectroscopy (ATR FT-IR). As an amphiphilic copolymer, PEG-b-PADS can self-assemble to micelles with PEG shell and PADS core in aqueous medium, and its self-assembly behavior and CO2-responsive properties were investigated by transmission electron microscopy (TEM) and dynamic light scatting (DLS). The size and morphologies of the micelles can be controlled by bubbling CO2 or Ar into the solution. Alternating treatment with CO2 and Ar could realize a reversible contraction-expansion transformation of the micelles. As a carrier for drug delivery systems, the micelles showed good controlled release behavior for drug molecules. Investigation shows that the release rate and level of doxorubicin (DOX) could be controlled through bubbling with CO2 and Ar alternatively.