Abstract: Cognitive decline is a common consequence of ageing, so age-related cognitive decline is considered normal or inevitable. For people over the age of 60, memory is more likely to be affected. With the extension of life expectancy, the number of people with age-related cognitive decline has also increased. Therefore, more attention has been paid to the improvement or mitigation of cognitive decline. Spermidine is a naturally polyamine, which involves many physiological processes, including neuroprotection learning and memory. Spermidine can maintain synaptic plasticity by inducing autophagy and immune regulation, which can promote neurogenesis and consolidate memory. It also has shown beneficial effects in aging biological models of neurodegenerative diseases. This paper reviews the current situation and relevant mechanism of spermidine in improving age-related cognitive decline, in order to provide reference for the prevention and treatment of age-related cognitive decline or other neurodegenerative diseases.