Based on Problem Solving Situation Theory，this paper builds a model of information seeking behavior of Weibo teenager users through questionnaires and structural equations，and analyzing the sex knowledge seeking behavior of this group，related ethics responsibility with the scientific communication path of sexual knowledge is also discussed. Data analysis shows that the factors of teenagers’ sex knowledge involvement and perceived knowledge are positively correlated with situational motivation，while the situational motivation of teenagers’ sex knowledge acquisition is positively correlated with information seeking. At present，the ethics problems of the subjective communication of sex knowledge mainly include the vague positioning of bloggers，the limited information contact of teenagers，the frequent occurrence of soft porn “marginal balls” and the loss of teenagers’ values. According to the above problems，this paper puts forward corresponding solutions.