The initial sedation practice in intensive care unit (ICU) which derived from anesthesia easily led to deep level or over sedation. However, with development of the research, deep sedation was gradually regarded to bring big harm to patients. So light sedation is recommended nowadays. However, the special target patients such as severe brain injury, persistent epilepsy, therapeutic low temperature and severe acute respiratory distress syndrome (ARDS) all need sedation in deep level. It is beneficial to treat most of critical ill patients with light sedation. To avoid unnecessary over sedation, strategies such as analgosedation, the protocolized sedation in goal of light level and early goal directed sedation are praised at present.