Abdominal fat thickness (AFT) is a crucial indicator for assessing fat deposition in White Feather broilers. Previous genome-wide association studies (GWAS) have primarily focused on single-point measurements of abdominal fat, with limited attention given to longitudinal phenotype records. Compared to traditional GWAS models, the longitudinal data-based GWAS (LONG-GWAS) model accounts for temporal phase effects, thereby more effectively controlling the false positive rate. This study conducted a genome-wide association analysis on 1654 White Feather broilers at four distinct ages during the laying period of broiler breeders (25, 27, 35, and 43 weeks). Three SNP loci associated with fat were identified (rs16341267, rs740644432, and rs15049519), which were annotated to three candidate genes: FDFT1, HTR2C, and ALDH3A2. These genes are involved in regulating lipid metabolism, energy balance, and fat deposition. This study provides new insights into the genetic basis of abdominal fat thickness in White Feather broilers and offers stage-specific marker information that can accelerate precision breeding for abdominal fat control in white feathered broilers.