Background: The phenomenon of "empty nest youth" is becoming increasingly ubiquitous, capturing the attention of society at large. However, few studies have been conducted in recent years on this group, especially focusing on their family and mental health. As such, this study investigates the correlation between family health and well-being among "empty nest youth," as well as the function of social support and loneliness in this relationship. Methods: A cross-sectional survey was conducted from June to August 2022 across 32 provinces, municipalities, and autonomous regions in China, utilizing a multi-stage sampling technique. And we screened individuals who were unmarried, living alone, and between 22-44 years old, resulting in a valid sample size of 908 cases; multiple regression analysis, mediation effect testing, and moderation effect testing are used to examine research hypotheses. Results: The regression analysis results show that family health not only has a direct impact on well-being (β = 0.36, p < 0.001) but also indirectly affects well-being through social support [β = 0.23, 95% CI: 0.19 0.28]. Additionally, the loneliness moderates the predictive impact of not only family health on social support (β = -0.13, p < 0.001) but also social support on well-being (β = -0.06, p < 0.001). Conclusions: These findings underscore the significance of directing policymakers and healthcare professionals towards the "empty nest youth's" familial and social support systems. It underscores the need for the development of policies aimed at addressing their emotional and material requirements by leveraging these familial and social networks. This approach ultimately contributes to the enhancement of their overall psychological well-being, promoting a more coherent and logical pathway for intervention and support.