The present invention discloses a series of compounds as CDK4 / 6 inhibitors. Specifically discloses the compounds of formula (I), their pharmaceutically acceptable salts or isomers thereof, the pharmaceutical compositions containing them, and the use in preparation for cancer treatment drugs thereof.本發明公開了一類作為CDK4/6抑制劑的系列化合物,具體公開了式(I)所示化合物、其藥學上可接受的鹽或其異構體、包含它們的藥物組合物以及它們在製備治療癌症藥物中的應用。