CSS(Conjugation-Suspention-Slipage) Law includes two aspects:Conjugation and Suspention-Slipage.Conjugation Law is discussed systematically in this paper.The concept of conjugation in chemistry is extended to philosophical category.The relationships between the two parties of contradictions and between all the electrological/non-electrological variables can be understood with the view of conjugation.Conjugation exists widely from microscopic to macroscopic world,from inorganic universe to organic universe and from biological universe to human society.The connotations of conjugation are analyzed deeply from the following aspects:category,properties,classifications and relation to other biological laws.The significance of conjugation to the cognition on human social practice is pointed out.