Abstract: To expand the proportion of the middle-income groups and construct olive-shaped income structure is an important goal in the new stage of China’s development, while to extend the duration of middle income is the main path for the expansion of the proportion of the middle-income groups. Based on the nine rounds survey data of CHNS from 1989 to 2011, and on the basis of the measurement of the middle-income groups, this study finds out that the time average of China’s middle income duration is 8.97 years, that the median is 7 years, and that there exists obvious negative time dependence. When the duration model which can control individual unobservable heterogeneity is adopted to analyze various influencing factors, the findings show that the individual characteristics, such as gender, age, level of education, types of work unit, and the regional characteristics, such as per capita GDP, Gini coefficient, unemployment rate, marketization degree, can produce significant effect on the duration of the middle-income groups. Meanwhile, the time of middle-income duration has significant urban-rural differences and regional differences. The conclusion believes that in order to improve the market prospect and opportunities for the low-income work force, it is necessary to construct a social security and welfare system covering the urban and rural residents and residents belonging to different work units. And different regional policies should be adopted against the structural characteristics of income mobility at different regions.

Key words: middle-income group; duration model; income structure; heterogeneity