Objective: To explore the interrelationships among fathers’ parenting effectiveness, urban children’s sociality and the acceptance of “second-born children” by children (including only children and “first-born children”), and to provide a reference for interventional measured for improving children’s acceptance rate of "second-bron children". Methods: Stratified cluster sampling method was used to select 3 to 9-year-old 778 only children and “first-born children” in two kindergartens and grades 1-3 of two primary schools in a city, and the children and their fathers were investigated with questionnaires survey regarding general information of both fathers and children, the acceptance degree of “second-born children”, the sociality of children and the parenting effectiveness of fathers. Results: Children in different grades had different acceptance levels of “second-born children” and the difference was statistically significant (F=2.89，P<0.05). Correlation analysis showed that the acceptance of “second-born children” was negatively correlated with the interaction between the only children and “first-born children”, and positively correlated with the prosocial behavior of the only children and “first-born children”, both of which are statistically significant (r=-0.10，0.10,P<0.01). Father’s role efficacy was negatively correlated with onlychildren and “first-born-children” peer interaction problems(r=-0.15), and positively correlated with prosocial behavior(r=0.32), both of which were statistically significant (P<0.01). The structural equation model of father’s parenting effectiveness, children’s sociality and acceptance of “second-born children” showed that low father’s parenting effectiveness could positively predict children’s peer communication problems and negatively predict children’s prosocial behavior, and thus children’s peer communication problems could negatively predict the acceptance degree of only children and “first-born children” to “second-born children”, and prosocial behaviors could positively predict the acceptance degree of “second-born children”. Conclusion Promoting father’s parenting efficiency can facilitate the social development of children and the acceptance of siblings.It’s recommended that fathers actively participate in specific parenting matters for the only child and "one child",and consciously improve parenting effectiveness.