Abstract: In order to evaluate the application potential of the rice resistance gene Pi9 in practical production, the dynamic changes of avirulence gene AvrPi9 of 396 Magnaporthe oryzae single-spore isolates collected from ‘LTH’ in Luoping County and Tengchong County of Yunnan Province from 2012 to 2014 were analyzed by artificial inoculation and PCR test. The results showed that the AvrPi9 frequency of the isolates reached more than 90% in the three years even with a declining trend, indicating that the resistance gene Pi9 could still be useful in the future, especially combined with the resistance genes Piz^t, Pi7 and Pi12, and the resistance association coefficients were all higher than 0.81. However, PCR amplification showed that 388 isolates carried AvrPi9 gene, among them 21 isolates contained the gene fragments but were still pathogenic to ‘IRBL22’ of Pi9 gene line, it implied the structure of AvrPi9 might be changing.