The historical context shows that populations move between regions and between urban and rural areas，causing a double transformation of economies and societies，that is， the history of the reform process and of industrial development is also testimony of social change. If we understand the inherent demand and rule of population migration，we can promote and accelerate the urbanization process and affect the interaction development of the society and economy. The traditional view is that the income gap will narrow with development of urbanization. This paper uses 1978-2009 provincial panel data and analyzes the flow of population migration，showing the dynamic mechanism and the reason ，the income gap between urban and rural areas for population migration . The income gap between urban and rural areas led to the unidirectional flow of population from rural to urban areas. People move from poor areas to rich areas，from rural areas to cities，but the income gap has widened and the growth of population migration is slowing，The inverted U-shaped relation of the income gap and population migration，if the income gap widens more，will affect the urbanization process. Research of regions show，The income gap between urban and rural areas in the middle and western regions has significant effects on population migration. The eastern region is not affected. This finding is a fact of the population migration in China.