In this study, a Cu/SAPO-18 catalyst was treated by H₂ reduction, which induced a remarkable enhancement of the low-temperature NH₃-SCR activity. Compared with the fresh catalyst, the reduced Cu/SAPO-18 catalyst showed an increase in NOx conversion from 45% to 80% at 175 °C, and from 80% to 100% at 200 °C, under a GHSV of 200,000 h^-1. The characterization (XRD, XPS and H₂-TPR) and in-situ DRIFTS results confirmed that a large amount of Cu cations (most of which were Cu⁺ ions) existed on/in Cu/SAPO-18 after the H₂ reduction treatment. The increased Cu^+/Cu²⁺ ratio led to the enhanced low-temperature SCR activity.