The invention provides a synergistic composition with sedaxane and Tolprocarb. The synergistic composition is characterized by comprising active components A and B. The active components A are the sedaxane and the Tolprocarb, the active components B are a type of metalaxyl-M, fludioxonil, prochloraz, hymexazol, silthiopham, ipconazole, triticonazole, triadimenol, diniconazole, efficient diniconazole, triflumizole, metconazole, myclobutanil, simeconazole, tetraconazole, difenoconazole, fenamidone, iprodione, fluoxastrobin, pyraclostrobin, azoxystrobin, trifloxystrobin, dinotefuran, imidacloprid, acetamiprid, thiamethoxam, nitenpyram, clothianidin, spirotetramat, chlorpyrifos, carbosulfan and ethiprole or compositions of more than one type of the metalaxyl-M, the fludioxonil, the prochloraz, the hymexazol, the silthiopham, the ipconazole, the triticonazole, the triadimenol, the diniconazole, the efficient diniconazole, the triflumizole, the metconazole, the myclobutanil, the simeconazole, the tetraconazole, the difenoconazole, the fenamidone, the iprodione, the fluoxastrobin, the pyraclostrobin, the azoxystrobin, the trifloxystrobin, the dinotefuran, the imidacloprid, the acetamiprid, the thiamethoxam, the nitenpyram, the clothianidin, the spirotetramat, the chlorpyrifos, the carbosulfan and the ethiprole. The synergistic composition further comprises auxiliaries which are allowed to be used during pesticide preparation processing. Conventional pesticide preparations can be prepared from the synergistic composition and can be applied to preventing and treating plant diseases and insect pests.