The previous scholars have pointed out that the sex structure has an impact on the organization operation and performance of organization members. In order to obtain a meaningful research results, the empirical analysis is conducted by means of single industry method. It is found that in small and medium-sized group practice accounting firms with simple businesses, the higher the proportion of female partnership accountants, the better profit performance their accounting firms will have. Moreover, when the proportion of female partnership accountants in small and medium-sized group practice accounting firms has a positive effect on its profit performance, the moderating effect is negative due to the different proportions of female employees. In other words, the proportion of female partnership accountants, the proportion of female employees and the profit performance of accounting firms have the significant negative interaction with each other. Therefore, it seemingly implies that the higher the proportion of female employees, the more negative impacts on profit performance of accounting firms.