Abstract: Objective To explore the sequential pathological changes during the process of establishing high fat diet fatty liver model in rats. Methods Sixty male Wistar rats （180-220 g） were divided randomly into six groups：normal control Groups （1,2,3）fed with common feed and model groups（4,5,6） fed with high fat feed （93.8% foundation feed,1% cholesterol,5% lard,0.2% bilesalt ）for 4,8,12 weeks. Results The liver index of the model group 4 is significantly higher than those of group 5，6 and normal control groups；but the liver index of the model group 5，6 is significantly lower than which of the control groups. The histological observation shows that the form of lipid droplet of the liver cell is mainly grain type, small bubble, large bubble in early, medium and advanced stage with the area of the vacuole significantly increasing one by one.The ultrastructural observation on the liver of the model groups' rats shows that the quantity of RER and SER is significantly different in each stage. Conclusion The lipid droplet form ，area of vacuole,quantity of RER and SER should be the evaluating indicator in the estimation of high fat diet fatty liver model,but the liver index and the variety of chondriosome lacks to be.