The invention relates to a polyethylene glycol/aliphatic polyester/cationic polymer amphiphilic triblock copolymer. The copolymer contains a hydrophilic non-ionic polymer block, a hydrophobic block and a pH-sensitive cationic polymer block. Potassium hydride is taken as an initiator, the polyethylene glycol and the aliphatic polyester monomers and the cationic monomer are sequentially added in a polymerization reactor for respective reaction, methanol is added for terminating the reaction; n-hexane is used for the precipitation and the purification of the triblock copolymer in tetrahydrofuran, the precipitation is repeated for 3 times, and a product undergoes the vacuum drying. The copolymer can form a micelle or a nanoparticle by self-assembly in a water medium, wherein, a core of a loading hydrophobic drug is formed by clustering the hydrophobic cationic polyester block, the polyethylene glycol block is assembled into a hydrophilic shell, thus having the functions of stabilizing the micelle and effectively avoiding the capture and protein absorption of a reticuloendothelial system of an organism; the cationic polymer block can be further acted with DNA, protein, peptide and other biological macromolecules, thus forming the biodegradable and pH-sensitive drug-loading polymer micelle or the nanoparticle which can be further dispersed,.