The invention relates to a bactericidal composition and a preparation method thereof. The bactericidal composition is characterized by containing a copper-containing agent and strobilurin, wherein the dosage of the copper-containing agent is 20-80 parts by weight and the dosage of the strobilurin is 1-30 parts by weight; the copper-containing agent is selected from at least one of the copper oxychloride, copper hydroxide, cuprous oxide, copper calcium sulphate, Bordeaux mixture and basic chrome sulphate; the strobilurin is selected from at least one of pyraclostrobin, azoxystrobin, fluoxastrobin, dimoxystrobin, kresoxim-methyl, picoxystrobin, enestroburin, fenaminstrobin, pyraclostrobin, phenylatestrobin, nitrobenzenestrobin, phenamacril, tricyclopyricarb, coumoxystrobin, pyrametostrobin and pyraoxystrobin. By adopting the bactericidal composition, the crop canker, the scab, the downy mildew, the angular spot, the epidemic disease and the gray mold can be simultaneously prevented and treated, particularly the red spider can be effectively prevented and killed; due to the synergistic effect of all components, the total controlling effect is greater than 80% and the drug resistance cannot be generated.