Due to their abundant nutrition and potential prebiotic functions, the potential development of oligosaccharide synthesis is very important. In this context, Synergistic catalytic manner of recombinant dextransucrase and Hypocrea lixii dextranase were elucidated according to carbohydrate analysis by carbohydrate gel electrophoresis and high performance liquid chromatography. The molecular weight of dextrans in the dynamic process of double enzymatic system with low concentrations sucrose showed an increasing firstly and then decreasing trend. High concentrations sucrose in dextransucrase and dextranase system led to accumulation of oligodextrans with molecular weight below 15 kDa. Comparative study of isomalto-oligosaccharides synthesis through both sucrose conversion and dextran hydrolysis was performed. Dextran hydrolysis through Hypocrea lixii dextranase gave rise to IMOs with degree of polymerization (DP) 2-15. Combined usage of recombinant dextransucrase and Hypocrea lixii dextranase produced isomalto-oligosaccharides with a DP range of 2-10, which showed great advantage and potential industrial value.