Objective To describe the characteristics of sexual debut among college students in China to provide appropriate sex education in that population. Methods An anonymous questionnaire survey was conducted among 33 653 college students selected by multi-stage stratified cluster sampling method in 18 provinces and cities of China. Results The percentage of students who had initiated sexual intercourse before age 14 was 1.9%. Overall, male students （2.8%） were significantly more likely to have initiated sexual intercourse before age 14, than female students （1.1%）. The percentage of students who had initiated sexual intercourse from age 15 to 18 was 6.4% in males versus 2.1% in females. while the rates of students who had initiated sexual intercourse after age 19 were 6.9% in males and 2.6% in females. The first sexual intercourse was significantly associated with parental educational attainment, geographic location and family structure. Students whose parents were relatively well educated, living in the western areas of the country China, or with nucleus/extensive families were more likely to have early sex in their puberties. Conclusion Sexual education should be strengthened especially in the western areas, and targeted on the students whose parents with relatively higher educational background or who were from extensive families.