Abstract: Despite the continuous decline in China’s overall birth rate, there exist significant disparities across different groups. Among them, migrant workers have a substantially higher fertility intention than pure rural households and urban residents. Therefore, strengthening research on the fertility intention of migrant workers is crucial for slowing the downward trend of China,s birth rate. Existing studies mainly analyze residents’ fertility behavior from the perspective of cost-benefit, and few explore the fertility decision-making of migrant workers from the altruistic motivation of intergenerational support. We examine the true impact and mechanism of overwork on the fertility intension of migrant workers using the data of CFPS. The study found that: firstly, migrant workers with overwork behavior have significantly higher fertility intension. This conclusion still holds after excluding issues such as sample self-selection, omitted variables, and reverse causality, and after a series of robustness tests. Secondly, the impact of overwork on the fertility intentions of migrant workers shows a clear asymmetry, particularly among male migrant workers, low educated migrant workers, and migrant workers who lack job security. Thirdly, overwork can increase actual income, strengthen job stickiness, and increase the possibility of intergenerational upward mobility, thereby leading to an increase in the willingness of migrant workers to have children. Fourthly, heavy-work may still increase the fertility intension of migrant workers, but its income effect is smaller than the crowding out effect caused by health loss, resulting in a significant decrease in the impact of heavy-work on migrant workers’ fertility intension. Fifthly, when migrant workers complete the identity transition from "outsiders" to "locals", overwork has a stronger promoting effect on their fertility intentions. However, after achieving identity transcendence, overwork no longer has a significant impact on their fertility intentions. This article provides a new explanation for comprehensively understanding the overwork behavior of migrant workers from the perspective of intergenerational support.

Key words: migrant workers, overwork, intergenerational support, fertility intension