Using survey data on migrant workers in urban China, this paper carries out a positive study on the impact of inner-industrial and inter-industrial job shifts on earnings growth of migrant workers. Results show that low human capital, low employment grades and low income are the most important reasons for migrant workers to switch jobs. The migrant workers who are young, unmarried new entrants with low level of education, no training and low income tend to change their jobs within the industry. And those who have high income and who find their jobs by themselves are more likely to switch jobs inter-industrially. Inner-industrial job switches have a significant positive impact on earnings growth of low-income migrant workers and a significant negative one on that of high-income migrant workers. Moreover, inter-industrial shifts have a significant negative impact on earnings growth of migrant workers of all income levels. The inner cause for the positive effect of inner-industrial shifts lie in the fact that the cumulative effect of years of service within enterprises is not obvious while continuing engagement in the same type of job within an industry will lead to accumulation of qualifications, which has a significant augmentation effect on earnings of migrant workers.