Objective <p>Obsessive–compulsive disorder (OCD) is a neurodevelopmental disorder, related to the central insulin signaling pathway. We investigate the relationship among central insulin signaling pathway gene polymorphisms/brain functional and clinical features in early-onset OCD(EO-OCD).</p> Methods <p>Candidate single nucleotide polymorphisms(SNPs) were genotyped and functional magnetic resonance imaging (FMRI) was performed EO-OCD and HCs. The MATRICS Consensus Cognitive Battery (MCCB) was used to evaluate those groups, and a mediating effect model to explore the relationship among polymorphisms-brain functional-clinical features in EO-OCD.</p> Results <p>In EO-OCD, Rac GTPase-activating protein 1(RACGAP1) rs297941 was the key polymorphism to insulin signaling pathway. The amplitude of low-frequency fluctuation (ALFF) in right precuneus were greater in EO-OCD patients with an A allele than the GG genotype and the ALFF in right supramarginal and postcentral was decreased. The functional connectivity (FC) between right supramarginal and left/right supplementary motor areas, between right cerebellum and left angular of inferior parietal border, and between left angular and right cerebellum was enhanced in A allele. The mediating effect model showed rs297941 influenced information processing speed and obsessive thoughts through intermediary effects of ALFF in right postcentral and enhanced FC between left angular and right cerebellum.</p> Conclusion <p>Rs297941 was signiffcantly to EO-OCD. Abnormal FC/ALFF play a mediating role between rs297941 and information processing speed in EO-OCD.</p>