To clarify the genetic diversity of tea plant germplasm resources in Wangcang County, Sichuan Province, and identify potential superior germplasms for new cultivar breeding, this study utilized a self-developed liquid-phase functional microarray for tea plants to genotype 76,252 SNP loci in 124 representative tea resources from Wangcang. Combined with biochemical component detection and organoleptic evaluation, the genetic structure and quality characteristics of these local resources were comprehensively analyzed. Genome-wide association studies were further conducted to identify SNP loci and candidate genes significantly associated with quality traits. The results show that the tea germplasm resources within the county exhibit rich diversity and distinct regional characteristics. Among them, the ancient tea plant population in Daliang is identified as a transitional type, rich in esterified catechins—particularly EGCG. The baked green tea produced from these plants demonstrates excellent quality, with a generally refreshing and high-aromatic profile featuring floral (or fruity) notes, and a taste characterized by sweetness, mellowness, and freshness, highlighting its significant breeding value. Based on 40,326 core SNP loci detected, four candidate genes highly associated with the content of amino acids, tea polyphenols, and EGCG were identified: γ-CA1, TPR5, MYB94, and UGT85A1. These results provide a theoretical foundation for the future development and utilization of tea germplasm resources in Wangcang.