Maltodextrin in specific length is of great interest because of its wide industrial applications. Previously, we have proven that Pyrococcus furiosus thermostable amylase (PFTA) produces high purity maltoheptaose (G7) from -cyclodextrin (CD) at early reaction time. In this study, an optimal continuous process for pure maltodextrin production from CDs using PFTA with immobilization in a packed-bed reactor (PBR) was developed. For testing PBR, -CD was used as a substrate to produce G7. The activity of immobilized PFTA in PBR retained 85% of the initial activity after 6 cycles, and the product purity was unchanged. The optimal conditions for the maximized G7-purity of 96.3% were predicted at 4.7 mL/min of flow, 1.1% substrate and 48.7 ◦C. Maltohexaose and maltooctaose, 92% and 97% purity respectively, were produced from CDs at the similar condition as well. Through this study, we successfully demonstrated the possibility of large-scale continuous production of pure maltodextrins from CDs.