The invention relates to the field of production of starch sugar, in particular to a composite glucoamylase preparation and a starch saccharifying method. The preparation comprises first saccharifyingenzyme and pullulanase, the first saccharifying enzyme is saccharifying enzyme secreted by aspergillus niger after an agdB gene is inactivated, and the enzyme activity proportion of the first saccharifying enzyme to the pullulanase is (7.5-80):1. By means of the composite glucoamylase preparation, a reverse reaction can be effectively reduced, and the obtained DX of the product is high; meanwhile, a saccharifying period can be greatly shortened, and a saccharifying window is prolonged.