Objective To investigate the effect of interleukin-17 (IL-17) gene polymorphism on the susceptibility to cow's milk protein allergy (CMPA) in infants and its association with gut microbiota. Methods A prospective study was conducted involving 100 infants diagnosed with CMPA at the Women and Children's Hospital of Ningbo University from January 2022 to October 2024. A total of 100 healthy infants undergoing routine check-ups at the same hospital during the same period was enrolled as the control group. Medical information was obtained through the electronic medical record system. IL-17A (rs2275913) and IL-17F (rs1889570) polymorphisms were detected using polymerase chain reaction-restriction fragment length polymorphism method. Serum IL-17 levels were measured using enzyme-linked immunosorbent assay, and high-throughput sequencing was employed to analyze the relative abundance of Lactobacillus and Bifidobacterium. Multivariate logistic regression analysis was used to explore the influencing factors of CMPA occurrence in infants. Results The proportions of infants with a family history of allergy and those with vitamin D deficiency or insufficiency were significantly higher in the CMPA group compared to those in the control group (P<0.05). The distribution of IL-17F (rs1889570) genotypes showed significant differences between the CMPA and control groups (P<0.05), with the frequency of the A allele being significantly higher in the CMPA group (P<0.05). Multivariate logistic regression analysis revealed that a family history of allergy, vitamin D deficiency or insufficiency, and carrying the IL-17F (rs1889570) AA genotype were independent influencing factors for CMPA in infants (P<0.05). Infants in the CMPA group with the IL-17F (rs1889570) AA genotype had significantly higher serum IL-17 levels compared to those with AG/GG genotypes (P<0.05), while the relative abundance of Lactobacillus and Bifidobacterium was significantly lower (P<0.05). Conclusions IL-17F (rs1889570) gene polymorphism influences susceptibility to CMPA in infants, potentially through mechanisms involving IL-17 expression and the relative abundance of gut probiotics.