Under the assumption that urban residents enjoy income from forms of capital return and based on neo-classical economic growth theory framework, this paper constructed the model of per capita income gap between urban and rural area, the analysis shows that, with the rising of urbanization rate, the multiple of urban-rural per capita income gap will gradually shrink, the bigger the share of capital return is, the bigger the multiple of urban-rural per capita income gap is, that the flowing of rural labor from rural to urban area will decrease urban-rural per capita income gap. Under socialism market economy framework, with free nationwide flowing of labors, both theoretical model and its deduction or empirical test results indicate that China’s income gap between urban and rural area is not enlarged but gradually shrinks.