The present invention discloses a kind of xylanase mutant and its preparation method and application, which relates to the technical field of genomic engineering and genetic engineering. Such mutant includes one or more mutants obtained by taking xylanase HwXy110A as female parent to conduct saturation mutagenesis to the site of Gly363. Specifically, relates to obtaining 19 mutants through site-directed mutagenesis, and then conducting yeast expression to them, after that, obtaining two mutants with significantly improved specific activity and thermal stability through screening of thermal stability and catalytic activity; the present invention can significantly improve the thermal stability and catalytic efficiency of xylanase through modifying the site of Gly363, and is of important guiding significance for improving the thermal stability and the catalytic efficiency of the 10th family of xylanases and other glycoside hydrolases as well as lays the foundation for its application in industrial production.