In order to study the effect of radiation on the Lagerstroemia indica seed and select new varieties with resistance to powdery mildew, the seeds were treated by 60Co-γ radiation and part of the plant of cuttage contrast tests were carried outed, the emergence rate, long stamens petalody, resistance and growth were investigated. The results showed that radiation treatment could significantly inhibit the emergence rate and had a certain role in promoting the petalody of long stamens. There were two plants with strong resistance to powdery mildew among the plants of Lagerstroemia indica ‘Liuyue Feixue’ that were radiated, and the others were infected with powdery mildew. Kangbing No.1 was immune to powdery mildew, and Kangbing No.2 showed high resistance to powdery mildew, ‘Sihai Shengping’ was moderately sensitive to powdery mildew, ‘Liuyue Feixue’ and ‘Redrocket’ were highly sensitive to powdery mildew. The plant height and groud diameter of the two disease-resistant plants were higher than those of the non disease-resistant plants, and the leaf fall period of disease-resistant plants were significantly later than that of non disease-resistant plants.