Based on the survey towards 250 migrant workers in Beijing，Guangdong，Jiangsu，Zhejiang and Sichuan and the interview of 10 migrant workers in Beijing，this study attempts to explore the basic status of sense of social fairness，the source of sense of social fairness，the response to social unfairness，and corresponding personal & social factors affecting sense of social fairness among migrant workers. The main findings from this study include：1.Generally speaking，all migrant workers in cities have felt unfair socially，there is no significant generational difference in this respect.2.The sense of social fairness among migrant workers not only comes from their personal feeling and experience，but also from what they see and hear personally .3.When migrant workers are treated unfairly，they usually adopt the coping strategy of passive escape. Meanwhile，there also exists the generational difference in safeguarding their legal rights.4.Multiple personal mental factors are related to their sense of social fairness significantly. These factors include status-justifying belief，outlook on fate，social comparison and attribution tendency.5.Social & historical process since 1949 and personal experience in social mobility are the main factors affecting the sense of social fairness among migrant workers.