Abstract: A model of data classification and protection is proposed by combination of knowledge ontology and rough set theories.Firstly,the data is classified in accordance with the business processes,and the knowledge ontology of classification is set up.And then,reduction of the attribute of the data is made by using rough set theories,and intelligent classification of the reduced data by using of the rules is done.Different protective measures are taken to different classification data.Furthermore,rough set theories are used to find rules from the historic data,and the knowledge ontology is studied.Finally,an experiment on a power system of a province is done as an example.The results show that the model can reasonably classify the data by the characteristics of different organizations.