Previous studies have examined the unbalanced distribution of opportunity cost of child rearing from the perspective of gender, but there is no further discussion about the parity and social stratum divergence of the cost among families and children. The paper uses the 5-period CFPS 2010-2018 longitudinal data to investigate the marginal opportunity cost of the second child and its stratification effect. It is found that bearing a second child requires a higher marginal opportunity cost for the families, especially in middle-income groups. In general, having a second child reduces a family’s income by 7. 1% and a wife’s chance of being employed by 9.3%; the corresponding statistics reached 8.6% and 20.5% in middle-income families respectively. From the perspective of economic rationality, the study provides a theoretical explanation and empirical experience for the depressed willingness to have a second child in modern families, especially for middle income classes.
