Powdery mildew is a devastating fungal pathogen that threatens wheat production. Identifying resistant germplasm and exploring resistance genes are crucial for sustainable improvement of wheat genetic resistance. Siyuehuang， a wheat landrace identified with resistance to powdery mildew from Shanxi Province’s wheat germplasm resources， was crossed with susceptible cultivar Jinmai 47. The segregation population was developed and subjected for artificial inoculation for resistance assessment and genetic analysis at seedling stage. We employed the bulked segregant analysis （BSA） combined with a 90K SNP array to locate the resistance genes. The resistance of Siyuehuang to powdery mildew was controlled by a single dominant nuclear gene （provisionally named PmSYH）， with an inheritance pattern in accordance with Mendelian inheritance law. SNP array analysis revealed that polymorphic SNP markers were mainly enriched in the 110 Mb to 140 Mb segment on the short arm of wheat chromosome 7D. SSR （Simple Sequence Repeats） molecular markers were developed in the interval， and six markers linked to PmSYH were obtained for genotyping the F₂ population. PmSYH was mapped in the physical interval of 132.6 Mb to 137.5 Mb， flanked by Sxau7DS-37 and Sxau7DS-48 with genetic distance of 1.8 cM and 3.1 cM， respectively. Comparative analysis with previous localization results suggests that PmSYH is a new resistant gene against powdery mildew. This study provided wheat new genetic resources for wheat resistance breeding， with a certain value for improving resistance to powdery mildew in the northern winter wheat region.