This paper investigates changes of dwelling income classes over time in New Town which has a distinct that new houses are simultaneously provided by public sector on a huge scale. As a result of the case study of Pan-Gyo New Town, according to the original master plan in 2004, they tried to mix various income classes in residential area and it seems that their intention produced desirable results in both social mix and filtering process in first move-in season 2009. But only two years later on a renewal of lease, it is changed to an abnormal community which only consists of high-income class and low-income class, and so that mid-income classes are disappeared. The major cause of the phenomenon is polarization of housing policy of government which is only just providing a large scale and high-class housing for high-income class or public housing for low-income class. If this situation continues, it will consistently happen the conflict between social classes such as social exclusion, social deprivation and be widespread social disorder.