The occupational segregation has been maintained for centuries in labor markets of various countries. Based on Social Dominance Theory, this research explained the occupational segregation phenomenon from social dominance orientation (SDO). And the author also aims to figure out the effect of sexism in this process. Due to the fact that each person and institution has different levels of social dominance orientation (SDO), men and women are inclined to choose the institutions whose values are identified with themselves. This process is called the self-selected mechanism of occupational segregation. Besides, when institutions face the choice of an employee, in order to maintain the priority of men, they do the same as individuals. According to Pratto et al, occupations can be divided into hierarchy enhancing ones and hierarchy attenuating ones. To explain more specifically, the hierarchy enhancing institutions are inclined to prefer men and the hierarchy attenuating institutions are more interested in women. It’s called the institution–selected mechanism of occupational segregation. We designed two studies to test the hypotheses above. In Study 1, the questionnaire survey was used to exam the relationship among gender, SDO and career choice. Data was collected from 187 students of Beijing Normal University. The result of Study 1 showed that men tended to choose hierarchy enhancing jobs and women tended to choose hierarchy attenuating jobs. Furthermore, SDO had a full mediating effect between gender and hierarchy jobs. The results indicated that occupational segregation had a self-selected mechanism, which means that men and women chose different jobs because of their different levels of SDO. In Study 2, an experiment was designed to test the relationship among SDO, sexism and hiring bias, in order to confirm the institution–selected mechanism of occupational segregation. 274 students from Beijing Normal University were recruited to do the tasks in study 2. They were asked to choose two resumes that best appeal to their respective institution in the capacity of an employer. One institution is a Securities Company, and the other is a charity organization. The results showed that hiring bias existed in different hierarchy institutions. The hierarchy enhancing institutions tended to choose male applicants and the hierarchy attenuating institutions tended to choose female applicants. Besides, both SDO and sexism could predict hiring bias, and sexism had a partial mediating effect between SDO and hiring bias. In conclusion, this research showed that during the forming process of occupational segregation, both self-selected mechanism and institution-selected mechanism are playing an indispensable part. This dynamic process provides us a new perspective to regard SDO and sexism, of which the former is not merely objective cognitions of group differences nor the latter is perceived social attitudes. In fact, they legitimize the inequality of social system. Through the connection of gender and different institutions and jobs, sexism and occupational segregation maintain in the society.