Toxicities of four fungicides to Alternaria alternate pathogenic bacteria was studied in order to select its control chemicals. The results showed that the four fungicides at different levels could inhibit pathogenic mycelium growth of Alternaria alternate. The inhibit effect of 40% Dimethachlon WP was best with the EC50 of 29.84 mg/L. The 50 % Nitrile bacteria triadimefon EC and 10% Polyoxins B WP were better, and the EC50 were 33.01 mg/L and 30.02 mg/L.While the inhibition effect of 10% Polyoxins(Polaroid Ann)WP was worst, the EC50 was only 139.42 mg/L. The bacteriostasis rates of 50 % Nitrile bacteria triadimefon EC, 10 %Polyoxins B WP and 40 % Dimethachlon WP were respectively 57.23 % , 66.52% and 67.44% , when ethephon concentration was 100 mg/L. While the inhibition rate of 10 % Polyoxins(Polaroid Ann)WP was only 45.39 %. Various fungicides inhibition rate also increase with the increase of concentration