The purpose of this study was to develop a statistical model of predicting item difficulty of the English reading test of College Scholastic Ability Test(CSAT). At the initial phase, the study investigated variables that were significantly correlated to item difficulty of English reading test. Using the correlated variables an instrument was designed to gather the data on item difficulty of each item of the English reading tests of 2002 and 2003 CSAT. Correlation analysis was done to get models which could predict item difficulty of the tests. To validate the results of the analysis, the models were applied to the September Tests of 2003 and 2004 CSAT. It was found that the 2003 linear regression equation model showed the acceptable level of stability and predictability. The study also revealed that statistically significant predictors were grammar, inference and options. It was also found that the proportion of variance accounted by the predictors was different. Some implications for CSAT design and further research were drawn from the findings.