Abstract: Cornell Net Carbohydrate and Protein System（CNCPS） is a set of new technology system that combines the latest research achievements and theories about the ruminal fermentation with the computer technology.And it showed a good practicability and superiority in the production.The researches on rumen micro-ecosystem,microorganisms,microorganism composition,ruminal fermentation,ruminal bypass,nitrogen loss and nitrogen cycle were expounded.From the former researches of CNCPS,the basic frame of the system was revealed,so as to provide reference for deeply understanding and applying CNCPS.