Objective To evaluate the prevalence of advanced colorectal neoplasm (ACN) in asymptomatic average-risk Chinese Han population, so as to provide a scientific basis for determining the optimal age for colorectal cancer screening. Methods A prospective cross-sectional design was used in this study. We used a self-made questionnaire to survey the average-risk adults receiving colonoscopy; the subjects were from 19 nationwide representative hospitals. The survey items included the demographic characteristics, life style, dietary habits, colonoscopy examination Results, etc. The risk of ACN was evaluated using previously established average-risk evaluation system, which was composed of eight variables: age, sex, smoking, diabetes mellitus, green vegetables, pickled food, fried food and white meat, with a total score of 0 to 14 points. We calculated the ACN prevalence of each risk level. The χ2-test was used to compare the prevalence rates of ACN between different risk levels, age groups and genders.Results A total of 7,541 subjects received complete colonoscopies. The ACN prevalence rose greatly with the increase of risk score. In the population with a risk score of 0-2, the ACN prevalence was 1.3%-4.0% in those younger than 70 years and 8.9%-15.3% in those elder than 70 years(P<0.01). In the population with a risk score of 3-4, the ACN prevalence was 3.6% in those younger than 45 years old and 5.4%-14.8% in those elder than 45 years (P<0.01). In the population with a risk score higher than 4, the ACN prevalence was at a high level (9.8%-22.7%), with the prevalence being 9.8% in the 40-44 years group, which was higher than those in subjects of 70-74 years old with a risk score of 0-2(8.9%). The overall ACN prevalence was 2.9%-4.6% in subjects younger than 55 years old and 6.8%-17.6% in those elder than 55 years (P<0.01). The high-risk age of ACN was elder than 45 in male and elder than 60 in female. Conclusion The optimal starting ages for colorectal cancer screening are different for subjects with different risks and genders. The starting ages for those with risks scores of 0-2, 3-4, and >4 were 70 years, 45 years and 40 years, respectively. The optimal starting age for screening in women can be 15 years later than in men.