This paper selected Taichung,Changhua,Tainan,Pingdong and other prisons in Taiwan,a total of 30 male inmates as research objects (All their crimes are compulsory and obscene,while the victims are their own daughters),using the phenomenological method of qualitative research and combined with in-depth interview research methods. It is concluded that the victim has the typical features of several kinds of common,and found that father-daughter incest is the most hidden and least known crime in all sexual assault cases,and analyzes the relationship between the crimes of incest fathers in Taiwan and their marital status,as well as the psychological cognition of father and daughter incest,and the motive of incest crime. The motives,causes and social conditions of incest crime of the father and daughterare provided to the education,social work and judicial departments and provide reference for the prevention and control of sexual crimes.