SnRK1 (SNF1-related kinase 1), a member of the SNF1 protein kinase superfamily, has been demonstrated to play a role in plant growth and development, as well as in stress responses. In this experiment, the leaf senescence of 'Xintaimici' cucumber was simulated by dark treatment and studied using SnRK1 activator/inhibitor and transient transformation technology. The effects of SnRK1 on cucumber leaf senescence, reactive oxygen species (ROS) metabolism, chloroplast structure, and photosynthetic characteristics were studied. The results demonstrated that the CsSnRK1 gene in cucumber leaves responded to dark-induced senescence. Furthermore, alterations in SnRK1 activity/expression affected the dark-induced leaf senescence process. Specifically, the activation of SnRK1 activity/expression can inhibit membrane lipid peroxidation by reducing the accumulation of ROS in leaves, slowing the decomposition of chloroplasts, repairing damage to photosystem II in leaves, delaying the senescence of leaves, and improving the photosynthetic capacity of leaves. Conversely, the inhibition of SnRK1 activity/expression had the opposite effect. These findings underscore the inhibitory role of SnRK1 in dark-induced cucumber leaf senescence. Our findings clarified the role of SnRK1 in regulating cucumber leaf senescence as well as its underlying physiological mechanisms, and will aid future studies of the molecular mechanism by which SnRK1 regulates cucumber leaf senescence.