In recent years, with the increasing of the NIMBY movements caused by urban middle class. Traditional Chinese academia usually regards the “middle class” as a “stable and buffer” device of social politics. It seems to be in accord with China’s social fabric, but in reality, it ignores the complexity and transition of Chinese political and social situations during the transition period. Based on a case study of “nuclear NIMBY movement” in R City, it is found that the social political functions of the middle class of the city may change at a particular time, or even appear two opposite states of “stabilizer” and “turbulence”. The internal mediation mechanism includes hierarchical class features and the risingtopower elite and, the external intermediary mechanism includes “the production of resentment” and “divergences within the government”, which is the deep mechanism of evolution of social and political function of the middle class. In addition, it is worth noting that, due to the “dual identity limit” and “system limit”, the social political function of the middle class often does not evolve into a “subversive dissimilation”.