The invention discloses a leucine dehydrogenase with an amino acid sequence shown in SEQ ID No.2 and a gene for coding the leucine dehydrogenase, and provides a novel dehydrogenase with a source different from that of a currently known leucine dehydrogenase. A leucine dehydrogenase gene ldh is cloned on the basis of a bacillus coagulans genome, has an amino acid sequence shown in SEQ ID No.1, and is used for coding the leucine dehydrogenase. The leucine dehydrogenase has very large advantages in preparation of optical pure amino acid and derivatives of the optical pure amino acid by catalytic asymmetric reduction of carbonyl. Meanwhile, the invention further provides a method for preparing, separating and purifying recombinant plasmids and recombinant bacteria with heat-resistant leucine dehydrogenase activity.