Objective: To compare behavioral and emotional health among first-born children and the only-child in Harbin, as well as associated factors including parents, family background, parenting and family environment. Methods: A questionnaire survey was conducted for 156 parents of first-born children and the only-children, matched in age (<3 months), class and gender. Achenbach Child behavior scale (CBCL), the Self-evaluation of Anxiety Scale (SAS), the Self-rating Depression Scale(SDS), the Parents Rearing Behavior Questionnaire (CRPR) and the Family Assessment Device Scale (FAD) were used. Results: There was no statistically significant difference in the scores of each dimension of children's emotional and behavioral health between the two groups(17.88±5.93)(19.13±6.01),total score(t=-0.74，P>0.05). There was no statistical difference in anxiety and depression between the two groups of parents(χ2=0.51，0.40，P>0.05); In terms of parenting style, the acceptance and encouragement achievement score for first-born children was significantly higher than that of the only child (t=2.10,2.12, P<0.05). In terms of family functions, there was no statistical difference in total function (t=-0.43, P>0.05). Behavioral problems associated with parents' anxiety, depression, parental rearing style and family function. Regression analysis showed that behavioral problems were mainly affected by sibling relationship for first-born children(B=8.74) and family role function for the only child (B=1.27). Conclusion No significant differences in behavioral and emotional health between first-born child and the only child are observed. However, harmonious sibling relationship, emotionally supportive parents and home environment could help improving behavioral and emotional health.