Abstract: Long-term continuous use of chemicals will cause drug resistance of Plasmopare viticola. By using leaf disc method, the toxicity of azoxystrobin, dimethomorph and their mixtures against Plasmopare viticola were tested. The results showed that the EC50 of 95% azoxystrobin, 98% dimethomorph and their five ratios (1: 1, 1:2, 2:1, 1:4, 4:1) was respectively 7.9003, 1.7656, 1.454, 1.685, 1.0117, 1.9688, 3.2009 μg/mL. The mixture of azoxystrobin and dimethomorph at the ratio of 2:1 had very strong inhibiting effect on Plasmopare viticola and could be used to control grape downy mildew in field experiment.