The cross-validation is probably the most popular approach for estimating the classification error rate in classifying gene expression data. In order to reduce the variance of estimation, the procedure of cross-validation will be repeated to get the average result. However, the repetition number of cross-validation is generally set by an empirical value. This paper proposed two methods (FCI and TSE) for determining the repeat number of cross-validation based on the approximate confidence interval. The experimental results on real data show the empirical method of giving repeat number of cross-validation is usually unreliable and the proposed methods can determine cross-validation repeat number to achieve a pre-specified precision of the error rate. Furthermore, both methods can automatically adjust to meet the change of data, the value of k-fold and classification model.