The present invention relates to a CDK4/6 kinase inhibitor, and a pharmaceutically acceptable salt, ester and solvate thereof or their stereoisomers； and also relates to a pharmaceutical preparation, pharmaceutical composition and kits which contain the CDK4/6 kinase inhibitor and the pharmaceutically acceptable salt, ester and solvate thereof or their stereoisomers； and the uses of the CDK4/6 kinase inhibitor and the pharmaceutically acceptable salt, ester and solvate thereof or their stereoisomers. For example, the compound of the invention can be used for reducing or inhibiting the CDK4/6 kinase activity in cells and/or treating and/or preventing cancer-related diseases mediated by the CDK4/6 kinase.
