The empirical likelihood approach is suggested to the pretest-posttest trial based on the constrains,which we construct to summarize all the given information.The author obtains a log-empirical likelihood ratio test statistic that has a standard chi-squared limiting distribution.Thus,in making inferences,there is no need to estimate variance explicitly,and inferential procedures are easier to implement.Simulation results show that the approach of this paper is more efficient compared with ANCOVA Ⅱ due to the sufficient and appropriate use of information.