Abstract: An in vitro procedure that simulated digestion in broilers was tested to evaluate the effects of graded level phytase adding in corn-soybean meal diet on broiler performance and phosphorus utilization. Phosphorus digestibility and amount of Inorganic Phosphorus (IP)release from 6 diets with and without graded level phytase were determined in vitro. Phosphorus digestibility and IP released were improved by adding phytase and go up with the increase of phytase level. Both of digestibility of phosphorus and IP released by in vitro digestion of low NPP diets with graded level phytase have high correlation with broiler daily gain, feed intake, phosphorus apparent digestibility in ileum, tibia ash , phosphorus in tibia and phosphorus in tibia ash of broiler (R²=0.971, 0.970; 0.990, 0.987; 0.962, 0.976; 0.903, 0.898; 0.866,0.859; 0.986, 0.984). So, we can get a conclusion that the in vitro digestion device for broiler can be used to evaluate and predict the effects of graded level phytase adding in broiler cornsoybean meal diets on broiler performance and phosphorus utilization.