Abstract: Sing-children family residing in two sides is a contingent form to adapt to the living needs for the single-child family in daily practice,and the nuclear family consisting of two single-children appears phantasm of double lineage institution.In fact,the phantasm hides a lot of problems.On the one hand,the boundary of successive identity cuts the single-child couple into two individual economic subject,and the binding of the son’s surname with inheritance tears the integrality of the nuclear family.On the other hand,because of interest,emotions and reality,the single-child couple has to moves between two parent-families,which makes their parents in a disadvantageous situation.Family supporting approximates formalized filial duty of grand funeral.In a word,the practice of single child residing in two sides changes the traditional lineage inheritance,leading to lots of potential problems.It is still unknown whether or not this change will lead to double lineage institution.

Key words: single-child, single-children families residing in two sides, contingency, potential problems, family institution