Abstract: This study aimed to investigate the effects of waterlogging stress on the morphological structure and physiological characteristics of Bougainvillea spectabilis 'Crimsonlake'. A pot waterlogging method was employed, and two-year-old potted seedlings of similar size and good growth condition were selected as the experimental materials. Four treatments were established: control（CK), root flooding（P1), partial flooding（P2), and complete flooding（P3). The growth status and physiological and biochemical indices of the bougainvillea were recorded and measured. The results indicated that waterlogging stress caused the atrophy of bougainvillea bracts, yellow spots, and drooping of leaves. The activities of superoxide dismutase（SOD), peroxidase（POD), and catalase（CAT）exhibited an initial increase followed by a decline. Malondialdehyde（MDA）content peaked at day 10 and then showed a decreasing trend. Compared to the control, the proline（Pro）content in treatments P1 and P2 increased, while in P3 it significantly decreased. The soluble protein（SP）content consistently decreased. Net photosynthetic rate（Pn), transpiration rate（Tr), and stomatal conductance（Gs）all showed a decreasing trend, with the most significant reduction in P3. Intercellular CO2 concentration（Ci）initially decreased and then increased. Comprehensive analysis revealed that bougainvillea can resist mild waterlogging stress. In the early stages of waterlogging, bougainvillea enhances enzyme activities and accumulates osmotic regulatory substances to combat waterlogging stress. However, prolonged waterlogging and severe waterlogging restrict its growth, with deeper and longer waterlogging leading to more pronounced inhibition.