Based on national sampling survey data from 2006, 2008, and 2011, the author uses the Mare educational transition model to systematically examine changing trends in inequalities in urban-rural educational opportunities at all educational stages from 1940 to 2010. Through a comparative analysis of five birth year groups, inequalities in urban-rural opportunities for elementary education were found to decrease, there were no changes in urban-rural opportunity inequalities for middle school education, inequalities in urban-rural opportunities in high school and other advanced secondary education continued to increase, and there was a slight increase in urban-rural opportunity inequalities at the college stage. The main conclusion of this paper is that urban-rural inequality in secondary education is the key location of educational stratification. The continued expansion of urban-rural opportunity inequality at the secondary education stage of transitioning from middle school to high school is the cause of decreasing relative opportunities of rural children to attend college. At the same time, the author verifies the industrialization theory hypothesis, reproduction theory hypothesis, and credentialism hypothesis, and the results of the data analysis support the reproduction theory hypothesis. [This article was translated by Jeff Keller.]