L-theanine (L-The) is a non-protein amino acid extracted from green tea. It has strong antioxidant activity and various pharmacological effects. For the central nervous system，L-The can improve cognitive function by directly promoting the occurrence of neurokines and indirectly resisting oxidation and other protective effects，which is beneficial to the treatment of AD. Besides，L-The，by exerting the characteristics of anti-oxidation and anti-inflammation，plays a role in neuroprotective agents. What`s more，it can also improve mood and sleep by increasing the activity of α wave and up-regulating the level of dopamine. For cardiovascular system，L-The can prevent cardiovascular disease by regulating NO level，regulating diurnal disorder and reducing LDL level. For tumor treatment，L-The can play an auxiliary role in anti-cancer by promoting tumor cell apoptosis and regulating the biological distribution of anticancer drugs；it can also protect multiple organs through anti-oxidation，including reducing drug damage to the body during treatment. For the immune system，L-The can increase the weight of the spleen，improve immunity，and reduce the risk of viral infection. For metabolism，L-The can also promote glucose metabolism and reduce the risk of type Ⅱ diabetes，and promote physical recovery after exercise. Because of its extensive pharmacological effects，L-The has a broad research prospect，which has been highly valued by scholars at home and abroad，and the related research is also gradually increasing. Based on the current research on pharmacology of L-The， the pharmacological effects of L-The on central nervous system，cardiovascular system，antitumor， reducing toxicity，immune system and metabolic regulation were reviewed. It is hoped that it can provide theoretical reference for the research and development of L-the and clinical medication.