;Institutional Research(IR) has been proposed for many years in the world . The main purpose of IR in college or University is to inform campus decision-making and plans in areas such as admissions, curriculum assessment , enrollment management , clubs , student life ,etc. The cause by changing of educational institution and social society, IR has been concentrate on many fields in recent years. Supporting assessment, strategic and decision-making effectively is the main topic in the thesis. The coverage of research topics of the IR is very wide. The thesis focuses on mining student causal rules consisting of city, high school types , admissions , clubs, permits , questionnaire survey of graduation .using those elements to find out rules base on suffix tree is appropriate. Building suffix tree through the bunch of factors which had been arranged in chronological order is the major method to discover effect rules . Mining the causal rules with the query interface to support IR researchers to determine decision-making accurately is the main purpose in the thesis.