The invention provides a mutant of penicillin G acylase (PGA) and a preparation method and application of the mutant. The non-rationally and semi-rationally designed enzyme engineering reconstruction technology is adopted for mutation of penicillin G acylase obtained from Escherichia coli ATCC 11105, so that a PGA mutant with higher reactivity, higher reaction rate, better conversion rate, stronger in penicillihe concentration tolerance, less substrate residue, and higher in phenyl acetic acid concentration tolerance; meanwhile, the mutant is subjected to recombinant expression, bacteria strain construction, fermenting cultivation, immobilization and application to prepare 6-amino-penicillanic acid (6-APA). The activity of the PGA-6 mutant prepared by the invention is increased by 102 times, the substrate penicillihe concentration tolerance is increased to 30%, and the phenyl acetic acid concentration tolerance is increased to 20 mmol/L; meanwhile, the immobilized PGA-6 mutant is used to decompose penicillihe with a concentration of 25% under the condition of pH 8.0 and 25 DEG C so as to prepare 6-APA, and the reaction time is shortened to 55 minutes, the substrate conversion rate is 98% or above, and after being used for 600 batches and above, the activity is not lost obviously, therefore, good operation stability is achieved.