Objective: To understand the status quo of sex education in left-behind children in rural areas. Method: Self-compiled questionnaires on sex education for left-behind children, teachers and general public and an interview questionnaire were administered to the target respondents. A total of 471 valid copies of questionnaire were retrieved, along with some interview data. Results: (1) There was a general lack of sex knowledge among left-behind children and hence a deficiency of the ability and consciousness to protect themselves; (2) School-based sex education was inadequate, and teachers believed that sex education should be strengthened at school; (3) There was a serious lack of family sex education, while the general public showed growing concern for sex education. Conclusion: It is necessary to strength sex education among left-behind children in rural areas from various dimensions, so as to elevate their sex knowledge and awareness about sexual health. The coordinated promotion by schools, families and society is an inevitable choice and an important measure to improve the effect of sex education.