Abstract Aim To construct a genetic landscape of infantile epileptic spasms syndrome (IESS) and explore the pathogenic mechanisms of IESS‐associated genes. Method We conducted a nationwide, multicentre, retrospective study across six centres in China, enrolling patients with genetically confirmed IESS between January 2015 and January 2024. Additionally, we reviewed the existing literature, summarized the genetic landscape of IESS, and used bioinformatics approaches to investigate its pathophysiological features. Results Our cohort included 430 probands with a genetic aetiology of IESS, with 394 of 430 (91.6%) carrying monogenic variants and 36 of 430 (8.4%) carrying copy number variants or chromosome abnormalities. A total of 168 genes were identified in 394 patients (219 males, 175 females; median age at epileptic spasms onset of 5.0 [interquartile range 3.0–7.0] months) with monogenic variants, including 14 genes that are not associated with any phenotypes in the Online Mendelian Inheritance in Man database. We compiled 354 IESS‐associated genes from our cohort and the related literature. The functions of these genes are related to membrane potential, synaptic signalling, and several ion channel activities. Interpretation We comprehensively mapped the genetic landscape of IESS and identified candidate pathogenic genes associated with the disorder.