After many years of development since the reform and opening up， migrant workers begin to have internal structural differences. For example， the income， capital and social network of the employed migrant workers are different from those of the self-employed migrant workers， and yet most of the researchers treat them as a whole. Meanwhile， a problem of statistical criteria inconsistencies has come into being in the current researches， which makes the data inconsistent both synchronically and diachronically， greatly reducing the information value of the data. So it is necessary to use consistent statistical criteria for structural analyses． Our definition of the employed migrant workers is based on a survey by the National Bureau of Statistics. The variation trend of the numbers and earnings of the employed migrant workers come from the National Rural Fixed Observation and China Statistical Yearbook. The main findings are as follows:（1） The number of migrant workers has stabilized， because the rising proportions of the migrant workers and the decreasing number of the rural workingage population have reached a relative equilibrium. The underlying reason is that urbanization and citizenization have made the rural population decrease quickly. （2） The number of employed migrant workers has increased slowly and begins to become stable. On the background of the stable migrant workers， the increase of employed migrant workers is due to a higher proportion of employment， which has risen to a very high degree. On the other hand， rural depopulation continues. Therefore， the number of migrant employed workers will also be stable， and it will even reach a ″turning point．″ （3） The proportion of young employed migrant workers （under the age of 35） has been declining year by year. One reason is that the proportion of rural young population has been rapidly declining， and another reason is that young migrant workers have higher employment expectations， which increases their difficulty in finding jobs．（4） The earning of employed migrant workers has a significant rise and it will continue to increase， but their earnings are lower than the average of all the migrant workers. In addition， the relative gap between urban workers and employed migrant workers has not narrowed down， which makes the problem of inequality worse．（5） There is a significant earning gap between the one with a high school diploma and the one with a college degree， and the gap is still widening.  This paper provides relatively accurate information for studying employed migrant workers， and the findings contribute to a better understanding of the structure of the migrant workers. It is hoped that further researches will be carried out in this area．