Objective To study the relationship between contraceptive knowledge, cognition and behaviors among vocational high school students.Methods A cross-sectional survey was anonymously self-administrated by way of computer to all the 1st graders among three vocational high schools in a district of Shanghai. Four cognition indicators, including perceived benefits, perceived barriers,perceived risks and self efficacy were applied according to Health Belief Model.Results The percentage of respondents who reported ever sexual practices and contraceptives use at first sex was 7.01% and 56.64% respectively. Condom (58.70%)and oral contraceptive pills (27.78%) were used by the majority. Main reasons for non-use were "shy to buy it" (26.53%) and "partner dont want to use any" (18.37%).Proportion of respondents who ever had sex regarded withdrawal and rhythm as effective were 68.35% and 68.42% respectively. Proportion of respondents having sex knew "Ifa person was infected with STDs, he/she might not have noticeable symptoms" were 22.86%. Proportion of respondents who reported non-use of contraceptives at first sex considered that "Infrequent intercourse could not cause a girl pregnant even she had experienced her menstruation" were 40.63%. Proportion of respondents who had ever used condom got full score of knowledge on "how to correctly use condom" were 23.26%. Perceived risks were poorest among four cognition indicators. High level of contraceptive knowledge was connected with high rate of contraceptives use at first sex, whereas high level contraceptive cognition was connected with high rate of contraceptive use both at first and recent sex.Conclusions It is important to provide youth-friendly services as well as message on contraceptives among vocational school students.