The invention relates to a Ralstonia strain as well as an application, a preparation method and a control effect evaluation method thereof. The Ralstonia strain is Ralstonia sp.56D2, and the strain is preserved in the China Center for Type Culture Collection on November 12, 2019; the preservation address is Wuhan University, Bayi road No.299, Wuchang District, Wuhan City, Hubei Province; the accession number of the strain is CCTCC No: M 2019921. The invention provides Ralstonia sp. 56D2 capable of preventing and treating tobacco bacterial wilt; a preparation method of the Ralstonia sp. 56D2; and an application of the Ralstonia sp. 56D2 in tobacco bacterial wilt disease.