Status legitimacy is that people perceive and believe the reasonability of existing hierarchy and the relationship between different hierarchies.Similar to other underclass，migrant workers in contemporary transition China are also struggling in a seemingly “legitimate” unequal status system. Taking the migrant workers in construction and decoration industry for example，this paper tries to reveal the antecedent mechanism which makes the unequal status legitimized. First，the subcontracting layers by layers and relationship hegemony personnel management practices in modern construction site build a hotbed for the traditional moral concept，which help workers accept the reasonability of the unequal hierarchy system. Second，the labor process is in accordance with accepted principles of social justice on the surface，which makes workers be more likely to recognize the status order reflected in this labor process.Third，the status legitimacy gains supports from external factors. Finally，the migrant workers in construction and decoration industry feel the superiority of their status situation in comparison with other groups，which also helps them get psychological balance.