The invention discloses a preparation method of a Trichoderma reesei gene engineering bacterium for highly yielding heat stability xylanase. The method comprises the following steps: synthesizing an expression cassette sequence sequentially comprising a Trichoderma reesei glyceraldehyde-3-phosphate dehydrogenase promoter, a Trichoderma reesei cbh1 signal peptide sequence, an xylanase xyn-LVK gene sequence and a Trichoderma reesei glyceraldehyde-3-phosphate dehydrogenase terminator; cloning the expression cassette sequence into pUC19 in order to obtain a recombinant expression plasmid; and lightly uniformly mixing the recombinant expression plasmid with a pAN7-1 vector, co-transforming Trichoderma reesei protoplasts, and screening the Trichoderma reesei protoplasts to obtain the Trichoderma reesei gene engineering bacterium for highly yielding heat stability xylanase xyn-LVK. The content of the xylanase xyn-LVK expressed in the Trichoderma reesei is about 40% higher than the content of the xylanase xyn-LVK expressed in Pichia yeast.