The present invention discloses a Salmonella paratyphi A with an O-antigen having an extended carbohydrate chain and uses thereof. The method comprises the following steps: inactivating an cld gene encoding an enzyme controlling chain length of O-antigen of a Salmonella paratyphi A strain to obtain a Salmonella paratyphi A with deletion of cld gene; allowing overexpression of cldLT2 gene encoding an enzyme controlling chain length of O-antigen of Salmonella typhimurium in Salmonella paratyphi A deficient in the cld gene encoding an enzyme controlling chain length of O-antigen, so as to extend carbohydrate chain length of O-antigen. Both of the Salmonella paratyphi A O-polysaccharide-recombinant fusion protein conjugate vaccines rCTB45733-OPSSpty50973 and rEPA4573-OPSSpty50973 as prepared by using Salmonella paratyphi A with an O-antigen having an extended carbohydrate chain can induce mice to generate specific antibodies against Salmonella paratyphi A, and their antibody titers are significantly improved.