Kernel-related traits, including kernel length, kernel width, and hundred kernel weight, are pivotal factors in determining maize yield. In this study, a recombinant inbred line (RIL) population derived from the maize inbred lines B73 and CML277 was utilized as the experimental material. Utilizing the high-precision genetic maps constructed through genotyping-by-sequencing (GBS) technology, nine kernel-related quantitative trait loci (QTLs) were identified, and qKW2.04 was precisely located on chromosome 2 using the inclusive composite interval mapping (ICIM) method, explaining 20.34% and 15.84% of the phenotypic variation, respectively. Building upon this, an F2 segregating population was developed using the recurrent parent B73 and its introgression line (NIL-1041A). This facilitated the further decomposition of major locus qKW2.04 into two major QTL, designated as qKW2.04-1 and qKW2.04-2. Through the selection of recombinant individuals within the target region, qKW2.04-1 was finely positioned within a 1.1 Mb interval. This study provides new clues for elucidating the genetic basis of kernel-related traits and gene resources for high-yield molecular breeding in maize.