Objective To investigate the correlation between functional constipation (FC) and the formation of fecaliths in the appendix cavity in children with acute appendicitis (AA). Methods The clinical data of children diagnosed with AA from August 2022 to June 2023 were retrospectively analyzed. According to the presence or absence of fecaliths in the appendix cavity, the patients were divided into the AA group with fecaliths and the AA group without fecaliths. The clinical characteristics of FC between the two groups were compared, and the factors affecting the formation of fecaliths in the appendix cavity of children with AA were analyzed. Results A total of 192 children (114 boys and 78 girls) with AA were included and the median age was 6.0 (4.0-9.0) years old. There were 72 children in the AA group with fecaliths and 120 in the AA group without fecaliths. Compared with the AA group without fecaliths, the AA group with fecaliths had a higher incidence of fecal retention (≥ 4 years old), higher prevalence of FC, longer average constipation time, and higher incidence of dietary bias, and the difference was statistically significant (P<0.05). Binary logistic regression analysis showed that prolonged constipation duration and dietary bias were independent risk factors for the formation of fecaliths in the appendix cavity of children with AA (P<0.05). Conclusions Long-term constipation and dietary bias have a certain correlation with fecaliths formation in the appendix cavity of children with AA.