The Interpretation (the 3rd) of the Marriage Law of P.R.C has been controversial since it was issued so far. The premise to solve this controversial problem is how qualitative analysis and theoretical expatiations can be carried out on the nature of Family Law which is the connotation of its legitimacy. The ethical nature is the nature of Family Law in qualitatively analyzing it either from the category of substance and forms or from the angle of legitimacy of Family Law. It is the key that the study on ethical nature of Family Law is emphasized on the theory of human nature that is the original starting point shared by Family Law and its ethics from a diachronic perspective. The human nature consisted of the animality and characteristics of man which is respectively involved physical and spiritual needs of man can be transformed into marital family ethics by moral evaluation mechanism and then homogenized into regulations of Family Law.