Wheat powdery mildew, caused by Blumeria graminis f. sp tritici (Bgt), is one of the devastating fungus diseases worldwide. Deployment of resistant cultivars is the most effective and environmentally safe approach to control the disease. Chinese winter wheat Bainong 64 conferred stable adult plant resistance (APR) in the past 30 years. In the current study, a population that included 171 recombinant inbred lines derived from a cross between Bainong 64 and Jingshuang 16 was used to dissect the genetic components and identify genomic regions associated with powdery mildew resistance. Based on 15K SNP chip, a genetic map comprising 1,635 frame markers (equal to 5,426 polymorphic SNPs) was constructed. Four stable quantitative trait loci (QTL) were identified on chromosomal arms 1DL, 2BS, 2DL, and 6BL in all five environments. The QTLs explained 4.4%-12.0% of the phenotypic variance and their favorable alleles all contributed by Bainong 64. All the QTLs were independent of plant height. The breeder-friendly KASP markers were successfully developed for the two QTLs of largest effects, QPmjbr.caas-2BS and QPmjbr.caas-6BL, and were tested on a 170 RILs population from Xindong 22 (fully susceptible to powdery mildew) and BFB 10 (a derivative of Bainong 64). The averaged maximum disease severity of the lines carrying resistance alleles at the QPmjbr.caas-2BS and QPmjbr.caas-6BL loci had significantly reduced values by 14.6% and 15.3%, respectively, compared with the lines with opposite alleles. The major QTL and KASP markers reported in this study will have significant values for the improvement powdery mildew resistance in wheat breeding.