In the research of cell cycle regulation, the knowledge of the functions of cyclinCDKs in the cell cycle regulation has been made a signifcant progress. Recently, the isolation and studies of the family of CDK inhibitor proteins, p16 and p21, imply that cyclins and CDIs form a very complicated cascad regulation network in the regulation of the activity of CDKs,through which they impose control upon the proliferation and differentiation of cell, are related to the formation and development of cancer.