The invention provides four gene deletion mutants of wild edwardsiella tarda (E.tarda) and derivative strains thereof. The four gene deletion mutants are respectively an E.tarda<deltaEvpC> strain with an EvpC gene losing function and derivative strains thereof, an E.tarda<deltaEvpCdeltaEsrB> strain with an EsrB gene losing function and derivative strains thereof, an E.tarda<deltaEvpCdeltaEsrBdeltaPstB> strain with a PstB gene losing function and derivative strains thereof, and an E.tarda<deltaEvpCdeltaEsrBdeltaPstC> strain with a PstC gene losing function and derivative strains thereof. 1-3 genes such as EvpC, EsrB, PstB, PstC and the like of the attenuated strains have parts causing loss of function or suffer from complete deletion, point mutation, shifting or insertion. Compared with a wild 1101 strain or other virulent strains, the E.tarda<deltaEvpC> strain, the E.tarda<deltaEvpCdeltaEsrB> strain, the E.tarda<deltaEvpCdeltaEsrBdeltaPstB> strain and the E.tarda<deltaEvpCdeltaEsrBdeltaPstC> strain have the advantage that the virulence does not exceed 1/40, 1/400, 1/4000 and 1/4000 of the virulence of the wild E.tarda 1101 strain or other virulent strains. The genetically engineered attenuated strains of E.tarda can be applied as attenuated vaccine strains of E.tarda, genetic engineering vectors or probiotics.