Provided are a theanine-producing strain and use thereof in tea fermentation production. A Corynebacterium glutamicum is proposed, which includes an alanine decarboxylase CsAlaDC mutant. The theanine-producing strain is obtained by taking the Corynebacterium glutamicum as a starting strain, knocking out in sequence an -ketoglutarate dehydrogenase E1 subunit gene odhA, a glutamate external transporter gene Ncg11221 and a lactate dehydrogenase gene ldh; and/or expressing a citrate synthase gene gltA, a pyruvate kinase gene pyk and a glutamate dehydrogenase gene gdh; and/or overexpressing an alanine dehydrogenase alaA and integrating a -glutamine synthetase GMAS into a cg1960 pseudogene locus of the Corynebacterium glutamicum.