A fluoxastrobin and pyraclostrobin compound suspension agent and a preparation method thereof. The invention relates to the technical field of prevention and control of cucumber downy mildew. The compound suspension agent is composed at least of 10 parts of fluoxastrobin, 30 parts of pyraclostrobin, 3 parts of styryl phenol polyoxyethylene ether phosphate triethanolamine salt, 2 parts of a naphthalenesulfonate formaldehyde condensate, 0.1 parts of xanthan gum, 0.1 parts of sodium benzoate and 0.1 parts of a defoamer, deionized water added to 100 parts. The preparation method includes the steps of pumping the raw materials into a blending kettle and mixing and stirring the raw materials; initially grinding the mixture through a colloid mill and fine-grinding the mixture through a sand mill, and collecting a sample and analyzing the sample; after the sample is qualified, filtering the processed mixture, metering a product, and packaging and storing the product. In the compound suspension agent, the ratio of fluoxastrobin to pyraclostrobin is 1:3 and the concentration of the compound suspension agent is 40%, so that the range of significant synergistic effect is reached, while preparations blended in other ratios cannot reach the range of the significant synergistic effect.