The present application relates to the field of enzyme engineering, especially relates to a pullulanase as well as preparation and use thereof. The pullulanase and coding gene thereof were obtained by random mutation by using the Error-prone PCR technique on the gene of wild-type pullulanase to obtain a mutant PLUM. The enzyme activity of the mutant PLUM was improved by 57.03% compared with the wild-type pullulanase PLUM.