A method and a special enzymic preparation for preparing ultra-high maltose syrup belong to the technical field of starch sugar generation and microbial gene engineering. The method is characterized by using fungusa-amylase RoAmy provided by the invention and using various plant starches as the raw materials and comprises the following steps: liquefying starch milk with high temperature resistantacid a-amylase, and then cooling the liquefied starch milk to 55-65 DEG C, adjusting the pH value to 4.5-6.5, adding the fungusa-amylase RoAmy and preserving heat for 30-60h, thus preparing 65-75% ofultra-high maltose syrup, wherein the gene of the fungusa-amylase RoAmy roots in rhizopus oryzae and the recombinant fungusa-amylase RoAmy is obtained by genetic engineering means. The invention alsoprovides a method for efficiently preparing yeast for the gene of RoAmy. In the method, the ultra-high maltose syrup is obtained by saccharifying starch with the fungusa-amylase RoAmy, and compared with the traditional preparation methods of ultra-high maltose syrup, the method of the invention has the advantages of simple process, low cost, benefit for amplification, etc.