Objective: To understand the current situation and influencing factors of sexual assault among middle school students, and to provide a basis for promoting healthy psychosocial environment for children and adolescents. Methods: A questionnaire survey was conducted among 1 471 middle school students in one city of Sichuan Province from April to May 2020 using multi stage stratified cluster sampling. Results: The proportion of middle school students who have been raped, indecent assault and sexual assault was 1.6%, 3.7% and 9.4%, respectively. About 23.8% of them had suffered two or more types of sexual assault; 75.1 % to 82.1% of sexual assault occurred between the ages of 9 and 15. Between 36.3% and 62.3% of sexual assault subjects were acquaintances of the same generation. Pornography exposure was the same risk factor for the three types of sexual assault (rape: OR= 9.93, 95%CI =3.09-27.57; sexual obscenity: OR=7.83, 95%CI =3.95-15.53; sexual harassment: OR=5.22, 95%CI= 3.52- 7.73, P <0.01). Low gender identity was the same risk factor for both suffering sexual obscenity and sexual harassment (sexual obscenity: OR=2.37, 95%CI =1.31-4.29; sexual harassment: OR=1.73, 95%CI=1.16-2.58, P <0.01). The long term absence of mothers was a risk factor for suffering sexual rape among middle school students ( OR=3.10, 95%CI =1.31-7.30), as well as father s sex education was a risk factor for suffering sexual obscenity among middle school students ( OR=2.52, 95%CI = 1.26 - 5.03 )( P <0.01). Conclusion Pornography exposure is the same risk factor for all types of sexual assault among middle school students. Low gender identity is the same risk factor for indecent assault and sexual harassment. Sexual education capabilities of families and schools should be improved, and attention should be paid to the gender identity and sexual mental health of middle school students.