Objective To understand the situation of sexual behavior and STD in floating population attending STD clinics Methods Floating population in STD clinics were investigated by questionnaires.Results Sexual behavior rate was 60.0% in unmarried floating population.Sexual behavior rate was 47.6% before marriage at the first sexual time.46.8% of the patients had more than 2 sex partners,and the rate of condom use among them was under 50%.STD prevalence rate was 37.1%,Re-infection rate was 12.2% accounting for 32.8% in all investigated STD patients.Conclusions It is importent to standardize service in STD clinics,provide health information,raise prevention knowledge,change their sexual attitude,advocate safety sexual behavior in various ways in high risk groups.