The invention belongs to the technical field of high molecular polymer materials for biomedicine, and discloses an amphiphilic pH-responsive 4 / 6 heteroarm star-shaped copolymer of which the number-average molecular weight is 30000-54000g / mol. The invention also discloses a preparation method of the amphiphilic pH-responsive 4 / 6 heteroarm star-shaped copolymer, which comprises the following steps: mixing epsilon-caprolactone, stannous octoate and low molecular initiator, reacting at 110-140 DEG C for 24-48 hours, performing reduced pressure distillation, precipitating, filtering, and drying to obtain polycaprolactone high molecular initiator; dissolving the polycaprolactone high molecular initiator, 2-diethylaminoethyl methacrylate, hexamethyltriethylenetetramine and copper bromide in toluene, stirring, then adding stannous octoate, and reacting at 60-90 DEG C for 5-12 hours; and adding methoxy polyoxyethylene methacrylate, continuously polymerizing for 5-12 hours, removing a catalyst, filtering, and performing posttreatment on the filtrate to obtain the amphiphilic pH-responsive 4 / 6 heteroarm star-shaped copolymer. The amphiphilic pH-responsive 4 / 6 heteroarm star-shaped copolymer is used for preparation of a micelle system for carrying water insoluble medicaments.