Background: To promote the balanced development with the population, China has phased out a one-child policy in 2016, and a twochild policy was launched, which has led to dramatic changes in family structure. The transition could be a huge challenge for adolescents who are in a period of psychological vulnerability. Purpose: This study explored the differences and predictors of family dynamics and functioning between two-child and one-child families in the context of China's two-child policy. Methods: We used the Self-rating scale of Systemic Family Dynamics (SSFD) and Family Assessment Device-General Functioning (FAD-GF) to investigate the family dynamics, family functioning, and family structure and status of 3289 adolescents under the background of China's two-child policy. Results: Results revealed that the mean scores for family atmosphere, personalization, disease concept, overall family dynamics, and family functioning health rate of the one-child families were higher than those of the two-child families. Parental marital status, mother's education, annual household income, and family economic satisfaction in two-child and one-child families was positively correlated with family dynamics and functioning, but not significantly associated with living style, parental age and employment. Family financial satisfaction, parental marital status, and distress in the family were predictors of family dynamics and functioning, and parental preference was also an important factor in two-child families.
Conclusion:The findings suggest family atmosphere, personality, disease concept, family dynamics, and family functioning of the one-child families were better than those of the two-child families. Unlike one-child families, parental preference is an important predictor of family dynamics and functioning in two child families. This study increases our understanding of adolescents psychological problems during family structure transitions under the background of fertility policy, providing psychologists with more evidence-based evidence and intervention directions.