This experiment was conducted to establish the mathematical model to estimate the digestibility of nutrients by the Cornell net carbohydrate and protein system (CNCPS) composition in the beef diets. In this experiment, four castrated beef bulls of the F1 generation from Angus×Luxi yellow cattle, which were 15 months old and weighed (311±22) kg, were used by 3×4 incomplete Latin square design. There were three different diets containing high (H), middle (M), low (L) energy level, respectively. But the contents of crude protein in three diets were the same. The compositions of CNCPS in different diets were determined. All the feces were collected to determine the total tract apparent digestibility of nutrients. The results showed that there were significant multiple regression relationships between nitrogenous compound and the digestibility of DM (R2=0.95, P<0.01), OM (R2=0.90, P<0.01), CP (R2=0.88, P<0.01) and ADF (R2=0.81, P<0.05) in beef diets, and there were significant multiple regression relationships between carbohydrate and the total tract apparent digestibility of DM (R2=0.90, P<0.01) and OM (R2=0.82, P<0.01) in beef diets. The results suggested that CNCPS could be used to estimate the total tract apparent digestibility of nutrients in beef diets.［Chinese Journal of Animal Nutrition, 2010，22（4）:929-933］