Under artificially-simulated complex salt-alkali stress, the levels of active oxygen metabolism in roots were studied using three-year-old cutting seedlings of Spiraea × bumalda Gold Mound and Spiraea × bumalda Gold Flame. The present study aimed at exploring the antioxidant capacity in roots of spiraeas and revealing their adaptability to salt-alkali stress. Results indicate that the oxygen free radicals contents, electrolyte leakage rates and MDA contents in roots of Spiraea × bumalda Gold Mound and Spiraea × bumalda Gold Flame show an increasing tendency with the increases of the salinity and pH value, whereas the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) all increased firstly and then decreased. With the increase in intensity of salt-alkali stress, the CAT activity in roots of Spiraea × bumalda Gold Flame is higher and the increasing extents in the oxygen free radicals contents, electrolyte leakage rates as well as MDA contents are lower compared with Spiraea × bumalda Gold Mound, indicating that Spiraea × bumalda Gold Flame has a stronger antioxidant capacity.