A method for synthesizing an aliphatic polyester block copolymer regulated by carbon monoxide. The method uses an organic cobalt metal complex as a convertible catalyst and includes: first regulating an anionic ring-opening copolymerization reaction between an aliphatic acid anhydride and an epoxy compound; then using carbon monoxide as a conversion agent for conversion to obtain a catalyst having a new catalytic active site; and regulating a vinyl monomer to perform active free radical polymerization to obtain an aliphatic polyester block copolymer having a controllable structure. The described synthesis method uses a convertible catalyst and a conversion agent, combines two controllable polymerization reactions which have different but compatible mechanisms, and obtains a block copolymer by means of a “one-pot” reaction.