The present invention discloses L-alanine dehydrogenase mutant zymoprotein and a preparation method thereof. According to a homologous sequence secondary structure comparison result, site-specific mutagenesis of 73th lysine near an L-alanine dehydrogenase activity center of Bacilluspseudofirmus into alanine through PCR is performed to construct a mutant expression vector, and prokaryotic expression and Ni-NTA affinity chromatography purification are performed to obtain a mutant enzyme K73A, wherein specific activity of the obtained mutant enzyme K73A is 202% of specific activity the wild type, and other enzymatic properties are not changed. In addition, a turnover number Kcat on a substrate L-alanine by the mutant zymoprotein is 376.7 min<-1> and is 2.0 times the turnover number Kcat of the wild type, a turnover number Kcat on beta-NAD<+> by the mutant zymoprotein is 290.1 min<-1> and is 2.1 times the turnover number Kcat of the wild type, and the mutant zymoprotein can be applicable for production processes of production of pyruvic acid, L/D-alanine, and the like through improvement biology methods.