The preparation conditions including transaminase (TGase) activity， treatment time and casein/ hemp protein isolate (HPI) ratios were optimized through response surface methodology (RSM). The in vitro digestibility， allergenicity and microstructure of the optimal complex were determined. The optimal cross-linking conditions were as follows: TGase activity was 31.90 U/g， treatment time was 2.06 h， and casein/HPI ratio was 10.51∶1.49. In this case， casein-HPI complex showed enhanced resistance to digestive enzymes and lower allergenicity before digestion or mild hydrolysis. In addition， TGase cross-linking changed the microscopic morphology of the protein， confirming the interaction between casein and HPI.