Abstract: Inheritance of resistance to powdery mildew（Sphaerotheca fuliginea, Beijing）in two inbred lines, WIS2757 from American and Jinyan 2 from China had been studied in the air conditioned greenhouse by spraying inoculum. The results showed that resistance genotype to powdery mildew in WIS2757 was RRssii, that means resistance was controlled by a major recessive gene s, a dominant gene R and an recessive gene i. The model was rrssii in Jinyan 2 that resistance was controlled by a major recessive gene s and a recessive inhibitory gene i, and differed from WIS2757 in gene R. The genotype of susceptible parent line was RRSSII.