This study analyzed the genetic resistance gene against P. xanthii race 1B in BC1 and F2 populations which were derived from a cross of resistant parent MR1 and susceptible parent Xinmi1 in melon. By taking use of the bulked segregation analysis (BSA) using molecular markers, the polymorphisms between both pools (R vs S) were revealed followed by preliminary mapping and marker saturation in fine mapping. The segregation analysis revealed a single dominant resistance gene Pm-M against powdery mildew on chromosome LG12, flanked by SSR12212 and InDel 2276. The physical interval containing Pm-M was delimited to 75.5-kb (Chr 12:22765111-22840651), where 16 genes were annotated. Among them, 12 genes were considered to be candidates underlying the powdery mildew resistance. Collectively, this study laid a foundation for map-based cloning of the disease resistance gene Pm-M and its use in breeding for disease resistance melon varieties.