The invention discloses a glutamate dehydrogenase mutant and an application thereof. The mutant is one of the following: a mutant of the amino acid sequence of SEQ ID NO. 1 which has a mutation at lysine at position 402 to phenylalanine or aspartic acid; a mutant which has a mutation at isoleucine at position 406 to phenylalanine or threonine; a mutant which has a mutation at threonine at position 121 and leucine at position 123; a mutant which has a mutation at alanine at position 379 and leucine at position 383. In the invention, the catalytic activity of glutamate dehydrogenase derived from Pseudomonas putida to 2-carbonyl-4-(hydroxymethylphosphonoyl)butanoic acid (PPO) is significantly improved by a molecular transformation method combining directed evolution and a semi-rational design; and the issue of low glutamate dehydrogenase activity in the process of preparing L-glufosinate by reductive amination is solved.