Using cross-sectional design▮twins and only children aged 6–16years were recruited. Using SDQ which was examined by parents and children (> = 11) to evaluate the children mental health and using EPQ applying on children to evaluate the children personality. the general questionnaire, PSDQ▮FAD-GFS▮SLE▮FSQ▮FLQ▮EFQ were used to collect information about family environment from parents. Zygosity was determined by the DNA picked up from cheek mucosa of twins children. Holzinger analysis was employed to estimate the heritability of personality and mental health. the stastic methods include t-test, nonparametric test, pearson correlation, spearman correlation.

122 pairs(244 children) of twins and 504 only children were participated in this study. the scores of four dimension of EPQ and five factor of SDQ have significant difference(Except for inattention-hyperactivity factor) between twin child and only child, the scores of EFQ,FLQ,FACES = 2 * ROMAN II-CV, FSQ, FAD-GFS have significant difference between the twins children family and the only child family.

Except for inattention-hyperactivity problems, there is obvious different in children personality▮mental health and their family environment between twin and only-child.