Fairness consideration is a vital drive in the social interaction, which has proven to be influenced by social identities. Poor-rich identity is quite special among different identities and people will tend to accept the injustice propose from the poor proposer. However, the mechanism in which poor-rich identity, an important one among social identities, can affect fairness consideration is still unknown. On the other hand, we also want to find out whether social entity justice could be the source causing the influences from proposer’s poor-rich identity. There are 2 experiments in the study. The Ultimatum Game was taken as the paradigm. The independent variables were 2 (proposer’s identity: the rich vs. the poor) * 3 (the level of justice: high vs. middle vs. middle). The dependent variable was acceptance rate. We found students in Shanghai Normal University randomly as our participants. The aim of study 1 was to discover the effect on fairness consideration from poor-rich identity. While in study 2 we added beneficial injustice and beneficial injustice transform to prove the existence of social entity justice and whether it could be considered as the source which caused the influences from proposer’s poor-rich identity to fairness consideration. In Study 1: We found that the main effect between the 2 identities was significant[F(1，22)=22.957，p<.001，ηp2=.511]and the result of the simple effect analysis indicated that the acceptance rate from the poor proposers was higher than from the rich ones(p middle=.005 ，p injustice<.001), so it meant that poor-rich identity could affect fairness consideration and participants tended to reject the unfair proposition from the rich. In Study 2: One result was that participants tended to refuse more the beneficial injustice proposes from the poor proposers(M=78.816，SD=6.626)than ones from the rich(M=92.105，SD=4.692)(p=.016).The other result was that the participants preferred to transform the beneficial injustice propose to the detrimental injustice propose(M=54.88，SD=46.479，t(41)=-2.906，p=.006，Cohen’s d=0.697). Those results suggested that social entity justice exist truly and it could affect fairness consideration as well, which meant that social entity justice could be the source of the effect from poor-rich identity on fairness consideration. To sum up, proposer’s poor-rich identity could influence fairness consideration and it played its role through the effect from social entity justice. The study 1 proved that poor-rich identity could affect fairness consideration, which suggested that it was more likely for people to reject the unfair proposition from the rich rather than the rich. The study 2 further the research by proving the existence of social entity justice and its effect on fairness consideration. People might defend the basic rights belonging to the poor. Furthermore, we could induce that social entity justice could be the source of effect from proposer’s poor-rich identity on fairness consideration. Concretely, if people hold social entity justice, they will reject the beneficial unfair proposition from the poor. In conclusion, the research proved that proposer’s poor-rich identity could affect fairness consideration and social entity justice was the source of the influence.