In the Outline of the Twelfth Five-Year Plan for National Economic and Social Development of the People's Republic of China, it proposed of improving distribution and form of urbanization and strengthening urbanization management. With acceleration of the urbanization, numerous rural labors flow to cities, and the number of left-behind children becomes increasingly large, which not only increases burden of family and education, but also gives rise to many mental problems. Due to lack of family education, many left-behind children have mental, emotional and ethical disorder and problem, which creates hidden trouble for building a harmonious society and economic development. This paper analyzed current situation and factors influencing mental health of left-behind children, including family environment, grandparent upbringing, and school environment. Finally, it came up with pertinent intervention measures from changing ideas of parents, improving the relationship between parents and children, and improving mental health education of schools.