Abstract: Different proportion of difenoconazole and tebuconazole mixed together can affect ustilaginoidea virens. In order to clarify different types of this combined effect, the inhibitory rate of mycelium growth of the pathogen and mycelium growth rate method are used to determine virulence to ustilaginoidea virens from difenoconazole, tebuconazole and their 5 matching ratios. The results indicated that EC₅₀ of ustilaginoidea virens was 1.568 and 21.487 mg/L, respectively, when affected by difenoconazole and tebuconazole, and indoor bioactive of ustilaginoidea virens influenced by difenoconazole was more than that influenced by tebuconazole. In the 5 different matching ratios of difenoconazole and tebuconazole, ratio 4:5 had the least EC₅₀, which was 1.858 mg/L. Ratio 1:8, 2:7, 3:6 and 4:5 had SR which were all above 1.5 and this illustrated these 4 matching combinations all had a synergistic effect towards ustilaginoidea virens. In addition, ratio (2-4): (7-5) produced SR greater than 2.0 and had the strongest synergistic effect. Difenoconazole and tebuconazole both had higher indoor bioactivity to ustilaginoidea virens, and the two with matching ratio of (2-4): (7-5) had the best synergistic effect towards ustilaginoidea virens. The suggested drug concentration was 117-375 mg/L.