The invention relates to a transaminase mutant with improved pH stability, belonging to the technical field of protein engineering. The saturated mutation evolution is carried out on high-flexibilityresidues (R131, P132 and E133) in a loop region above an active pocket through analysis of a transaminase crystal structure, three mutants (R131A, R131C and R131D) are acquired through high-flux screening, and the corresponding amino acid sequences of the mutants are sequentially SEQ NO.2, SEQ NO.3 and SEQ NO.4. The transaminase mutant with the improved pH stability is capable of preserving high catalytic activity under a pH of 9.5, so that the industrial utilization potentiality of transaminase in chiral amine medical intermediates is further improved.