The invention discloses a pesticide composition and an application thereof in prevention and treatment of potato common scab. The pesticide composition comprises a rhodopseudomonas palustris biocontrol inoculant and a bactericide; the bactericide is a dithiocarbamate bactericide. The pesticide composition comprises the rhodopseudomonas palustris biocontrol inoculant and the bactericide; on the premise of reducing the application amount of the chemical bactericide, the rhodopseudomonas palustris biocontrol inoculant is supplemented and applied, the advantages of the chemical pesticide and the biopesticide can be exerted respectively, preferred complementation and synergistic interaction can be realized, various bacteriostasic mechanisms can be integrated to effectively control the occurrence of diseases, the pesticide resistance risk and phytotoxicity can be effectively reduced, and the influence on the environment can be reduced to the greatest extent. Moreover, the rhodopseudomonas palustris biocontrol inoculant has the advantages of environmental friendliness, no toxicity to human and livestock, no phytotoxicity to crops, simplicity and convenience in application and the like, and is not easy to cause drug resistance to plant diseases and insect pests.