Abstract: The aim of this experiment was to identify the pathogen of Corn Northern Leaf Blight and screen out the best bactericide for controlling Corn Northern Leaf Blight,the method of tissue separation was used to isolate and identify the pathogen, and the culture medium growth rate Method was used to determine the inhibitory effect of seven kinds of fungicides on pathogens of Corn Northern Leaf Blight. the pathogen was identified as Alternaria alternate (Fr.) Keissl, toxicity test results show that: after 48 h, the EC50 of Iprodione was 0.27 mg/L;the virulence index was the highest, and the inhibitory effect was very significant; the EC50 of Propiconazole and Difenoconazole were 0.51 and 0.53 mg/L, and their inhibitory effect were significant; the EC50 of Flusilazole and Pyrimethanil were 1.66 and 1.91 mg / L, and the effects were good; the EC50 of Mancozeb and Kresoxim-methyl were 25.82 and 929.78mg / L, their virulence index were low and inhibitory effects were poor;the inhibitory effect was similar between 72h and 48h;therefore,the inhibition effect of Iprodione on Alternaria was the best among the seven fungicides, When the experiment concentration was 50 mg/L, the inhibition rate was 95%.