[Purposes] The paper aims to enrich the categories of starch debranching enzymes, make full use of starch resources, and realize the efficient preparation of starch deep?processing products such as glucose, maltose, cyclodextrin, etc., a dextrin debranching enzyme (DDE) derived from the extreme archaea (Thermococcus gammatolerans，abbreviated as T. gammatolerans) was investigated. [Methods] The physicochemical properties and structure prediction of DDE from T. gammatolerans were carried out by bioinformatics analysis tools, and then molecular biotechnology was used to achieve its extracellular secretion expression in Escherichia coli （abbreviated as E. coli）. Moreover, the enzyme yield was improved by optimizing fermentation temperature, fermentation time and the amount of inducer added. [Findings] DDE from T. gammatolerans is a hydrophilic protein with high stability, and no signal peptide is included in its amino acid sequence. The enzyme DNA sequence was constructed into pET?20b(+) vector containing a signal peptide, which contributed to achieve its protein expression and extracellular secretion in E. coli BL21(DE3). The optimal fermentation conditions were as follows: the seed medium cultured at 37 ℃ for 12 h was inoculated into TB medium, and isopropyl?β?D?thiogalactoside with a final concentration of 0.01 mmol/L was added to induce expression at 25 ℃ for 84 h. Under the control of these conditions, the extracellular enzyme activity of DDE was 326.0 U/mL, which was 1.36 times higher than the initial enzyme activity. [Conclusions] DDE from T. gammatolerans has excellent physical and chemical properties as well as a high expression level, inclining that this enzyme has potential application value in the industrial sugar productions of starch.