Abstract: In order to screen the genetic markers and candidate genes associated with the weight of the longissimus dorsi in Huaxi cattle and Snow Dragon black cattle, genome-wide association study（GWAS） was conducted on the weight traits of the longissimus dorsi in 1 478 Huaxi cattle and 452 Snow Dragon black cattle. The phenotypic data of longissimus dorsi muscle weight after slaughter were measured, and the genome was genotyped by Illumina Bovine-HD（770 K） chip. The GWAS was performed on the chip data after quality control using FarmCPU model and GEMMA model to explore the SNP loci and candidate genes significantly associated with the longissimus dorsi muscle weight of Huaxi cattle and Snow Dragon black cattle. The results showed that the phenotypic traits of longissimus dorsi muscle weight of Huaxi cattle and Snow Dragon black cattle were in accordance with the normal distribution. After quality control, 607 198 and 511 320 SNP loci were obtained from the microarray data of Huaxi cattle and Snow Dragon black cattle, respectively, and the distribution of these SNP loci was relatively uniform on each chromosome. By using the FarmCPU model, 12 and 9 SNP loci significant associated with the longissmus dorsi muscle weight were detected in Huaxi cattle and Snow Dragon black cattle populations, respectively, and the SNP loci in Huaxi cattle population were located on chromosomes 1, 5, 7, 11, 12, 13, 15, 16, 22, 23.Twenty candidate genes were identified, including KCNAB1, PFN2, RNF13, TTLL1, MCAT, CREB3L3, ZBTB7A, MAP2K2, CAMKMT, ZC3H13, OPTN, MCM10, UCMA, OVOL2, PET117, KAT14, MAML2, HHAT, FHIT and LY86. The SNP loci of Snow Dragon black cattle were located on chromosomes 4, 16, and 27, respectively, and three genes（PCLO, DCTD, and WWC2） were identified. Six SNP loci significant associated with the longissimus dorsi muscle weight were detected in both Huaxi cattle and Snow Dragon black cattle populations by GEMMA model. The SNP loci in Huaxi cattle population were located on chromosome 13, and GATA3, TAF3, ODAD2, SNX5, MGME1, OVOL2, KAT14 and PET117 genes were identified. The SNP loci of the Snow Dragon black cattle are located on chromosomes 1, 4, 5, and 25, repectively, but no valid candidate genes have been identified. The 18 and 15 SNP loci detected and the 25 and 3 candidate genes annotated in the populations of Huaxi cattle and Snow Dragon black cattle could serve as new molecular markers and candidate genes for improving the weight of the longest back muscle in beef.