To investigate the relationship between the measurement of the distance between the lesion and the anal margin and the lesion location under fibercolonoscopy in colorectal cancer.

The clinical data of 5031 patients who underwent colorectal cancer surgery from January 2013 to December 2020 were retrospectively collected. SPSS 25.0 software was used for data analysis，and count data were expressed as absolute numbers or percentages. The median M（P25，P75）was used to represent non-normally distributed measurement data. Mann-Whitney U test was used for comparison between two groups，Kruskal-Wallis H test was used for comparison between multiple groups，and Bonferroni method was used to correct for pairwise comparison of significance level. P<0.05 was considered statistically significant.

The distance distribution between the tumor and the anal margin was measured by fiber colonoscopy as follows：Cecum 70（65，75）cm，ascending colon 70（60，75）cm，liver curvature 70（60，75）cm，transverse colon 60（50，70）cm，splenic curvature 50（40，60）cm，descending colon 40（35，50）cm，sigmoid colon 21.5（18.5，30）cm，rectum 8（5，11.5）cm . There were significant differences in the distance between the lesions of different parts and the anal margin（P<0.001）. After pairwise comparison，there was no significant difference between the measured distances of tumors in each part of the right colon（P>0.05）.

The distance between the tumor and the anal margin measured by fiber colonoscopy before surgery cannot strictly distinguish the distribution of tumors in various parts.