Abstract: In order to identify the pathogen and host plant species of tobacco powdery mildew in Luoyang tobacco-growing area, the tobacco powdery mildew pathogens collected from Luoyang tobacco-growing area were identified by morphological observation and molecular biological determination. The host range in Luoyang tobacco-growing area was determined by combining pathogenicity evaluation with molecular biological analysis. The results showed that: 1) The pathogen of tobacco powdery mildew in Luoyang tobacco area was Golovinomyces tabaci. 2) In addition to tobacco, 22 kinds of powdery mildew pathogens collected from plants infected with powdery mildew around tobacco fields were not G. tabaci and those pathogens had no pathogenicity to tobacco. 3) The collected tobacco powdery mildew pathogen was pathogenic to plantain and pea, which were two plants in 22 common plants around tobacco fields. The results of molecular biological identification further confirmed that plantain and pea were the host plants of tobacco powdery mildew pathogen in Luoyang tobacco-growing area.