This study was conducted to simplify the assessment technology of intestinal absorbed amino acids fluxes of rumen undegradable protein (RUP) based on Cornell net carbohydrate and protein system (CNCPS). Intestinal absorbed amino acids were consisted of microbial protein and RUP. Crude protein (CP) was divided into A, B1, B2, B3 and C in CNCPS based on solubility, only B fractions could pass rumen and be digested in intestine. To estimate the contribution of intestinal absorbed amino acids from RUP, CNCPS model needed the degradability of B fractions, and intestinal digestibility of B fractions used different constants. This study collected 18 kinds of feedstuffs including 12 kinds of concentrate and 6 kinds of roughage. The data for measuring RUP intestinal absorbed amino acids fluxes in CNCPS was determined, and it was also determined that ruminal degradability of CP and intestinal digestibility of RUP at different time points. Based on the above data, simplification methods were concluded. The results showed as follows:1) CP ruminal degradability at 8 h (X,%) and effective degradability (Y,%) got the highest correlation with linear correlation both in concentrates and roughages. The equations for concentrates and roughages were Y=12.652+0.828X, r=0.990, P<0.000 1 and Y=10.967+0.886X, r=0.980, P=0.000 6, respectively. 2) CP intestinal digestibility of residues retained in rumen for 2 h (X,%) got the highest correlation with RUP intestinal effective digestibility (Y,%) for concentrates, and the equation was Y=0.026+0.879X, r=0.970, P<0.000 1; CP intestinal digestibility of residues retained in rumen for 8 h (X,%) got the highest correlation with RUP intestinal effective digestibility (Y,%) for roughages, and the equation was Y=-0.002+0.960X, r=0.995, P<0.000 1. 3) After reliability assessment, the highest correlations were found in intestinal absorbed amino acids predicated by simplified CNCPS models using ruminal degradability and CP intestinal digestibility of residues retained in rumen at 8 h (X, ‰) and CNCPS (Y, ‰), and the equations for concentrates and roughages were Y=-0.056+1.409X, r=0.999, P<0.000 1 and Y=0.003+2.120X, r=0.999, P<0.000 1, respectively. The root-mean-square phase errors were 0.245 and 0.005, respectively, and the coefficients of variation were 7.08% and 4.49%, respectively. In conclusion, simplified predation models for RUP intestinal absorbed amino acids fluxes are set based on CNCPS, and the simplified modes for concentrates and roughages are Y=-0.056+1.409×[AA×(100-D₈)×CP×ID₈], r=0.999, P<0.000 1 and Y=0.002+2.120×[AA×(100-D₈)×CP×ID₈], r=0.999, P<0.000 1, respectively[Y is RUP intestinal absorbed amino acid flux (‰), D₈ is CP ruminal degradability at 8 h (%), ID₈ is RUP intestinal digestibility at 8 h (%), AA is amino acid content in insoluble protein (%)].