The purpose of this study was to analyze the results of the achievement test of adding and subtracting with unlike denominators for the fifth grade students from one elementary school in urban area of Tainan City, and to investigate the relationship between gender and different types of representation. In this study, data was collected through the achievement test designed by the researcher. Statistical methods of Descriptive statistics, Independent Sample t test, Paired Sample t test and Two-way ANOVA were then employed to analyze the performance of the different gender of the fifth grade students, the performance of the fifth grade students on the different types of representations, and whether there were interactions between different gender and different types of representations.The research results were as follows: 1. The results of item analysis on the achievement test of adding and subtracting with unlike denominators for the fifth grade students: (1) The average pass rate for the test is 66%. (2) The average fail rate for the test is 34%. (3) The error patterns include fractional addition errors, Expanded fraction errors, conceptual errors, and etc. 2. There was no significant difference between gender among the fifth grade students in the performance of the achievement test on adding and subtracting with unlike denominators. 3. There were no significant differences among the fifth grade students on the different types of representation of the achievement test on adding and subtracting with unlike denominators. 4. There were no remarkable interaction effects between different types of representations of adding and subtracting with unlike denominators and different gender.