Trained immunity（TI），independent of the T and B cells and distinct from the characteristic of traditional innate immune，is a memorial innate immune response. The organism can show increased responsiveness upon subsequent stimulation with the same or a different stimulus，well after the initial challenge. Trained immunity，as a new concept，involves the interaction of innate immune and the metabolic and epigenetic mechanisms. Based on this，this article summarized the effects of stimulation such as lipopolysaccharide（LPS），bacille calmette-guerin（BCG），and hormones on epigenetic and metabolic modifications of innate immune cells such as monocytes/macrophages，natural killer cells and non-classical immune cells，and explored the long-term vision of modulating training immunity in inflammation，nervous system diseases and COVID-19.