Abstract: 【Objective】 This study aims to develop and validate KASP molecular markers closely linked to melon downy mildew resistance genes, in the hope of providing a theoretical basis for downy mildew resistance molecular marker assisted breeding of downy mildew resistance in melons. 【Methods】 The accession ‘PI 438685’ with high resistance of downy mildew, and the accession ‘Huangdanzi’ with high sensitivity of downy mildew were used as parents to construct a separate population.QTL mapping of downy mildew resistance genes in melon was drawn through a combination of BSA and whole genome sequencing.KASP molecular markers closely linked to downy mildew resistance genes were developed within this interval, and then screened and validated using F₂ separate populations. 【Results】 The downy mildew resistance gene was located on chromosome 9 through BSA analysis.We developed 66 pair of KASP molecular markers in the candidate region, screened 9 pairs of KASP molecular markers with high specificity.Subsequently, the 9 pairs of KASP molecular markers were validated, the KASP molecular marker (KASP-24832572), closely linked to downy mildew resistance genes was obtained, and its accuracy of distinguish genotype could reach 79%. 【Conclusion】 One QTL related to downy mildew resistance has been located on chromosome 9 by BSA analysis, and a pair of KASP molecular markers closely linked to downy mildew resistance genes are developed in this interval, which has contributed to downy mildew resistance breeding in melons.