In order to elucidate the molecular mechanism of lettuce seed germination under heat stress， the transcriptome， metabolome and multi-omics combined analysis were performed on the seeds of two lettuce varieties， heat-tolerant cultivar Italian Lettuce and heat-sensitive cultivar Four-Season Fodder Lettuce. Untargeted metabolomics identified 391 differentially expressed metabolites （DEMs）， revealing specific activation of the tyrosine metabolism and flavonoid biosynthesis pathways. Metabolites including muconic acid， L-tyrosine， L-tyramine， and p-hydroxycinnamic acid were significantly enriched. Transcriptome analysis detected 3127 differentially expressed genes （DEGs）， indicating two distinct genetic regulatory mechanisms associated with early thermotolerance in lettuce germination： （1） Unique upregulation of heat shock protein （HSP）-related genes in Italian Lettuce； （2） Activation of β-glucanase-coding genes by AP2/ERF transcription factors， facilitating repair of heat-damaged cell walls. Key candidate genes were initially screened using Gene Set Enrichment Analysis （GSEA） combined with protein-protein interaction （PPI） network analysis. qRT-PCR validation corroborated the RNA-seq findings. Integrated multi-omics analysis demonstrated significant downregulation of ethylene biosynthesis genes （ACO， 1-Aminocyclopropane-1-Carboxylate Oxidase） in Four-Season Fodder Lettuce. Concurrent suppression occurred in core flavonoid pathway genes， β-glucosidase-encoding genes， and biosynthesis of aromatic amino acids （tyrosine）. These results indicate that heat stress inhibits seed germination through a dual mechanism involving metabolic flux blockage and inactivation of the antioxidant defense system. This study delineates the gene-metabolite regulatory network underlying the heat-stress response during lettuce seed germination， providing a theoretical foundation for the molecular interactions governing germination inhibition.