The technological processes and conditions of preparing casein phosphopeptides (CPPs) from casein were studied. Taking contents of N and P as indexes, the optimum conditions of preparing CPPs by the action of trypsin were established with orthogonal tests. The optimum temperature was 40℃, the hydrolytic time was 80 min, the concentration of casein was 15%, and the ratio of casein and trypsin was 100∶1.