Objective To quantify the degree of unconsciousness with EEG nonlinear dynamics analysis and investigate the changes of EEG nonlinear properties under different statuses in unconscious anoxia-ischemic patients. Methods Thirty unconscious anoxia-ischemic cases were selected as the patient group. Thirty normal conscious patients with stroke were involved as the control group. EEG was recorded under three conditions, including eyes closed, auditory stimuli (verbal and music) and painful stimulio. Nonlinear indices such as correlation dimension, complexity and approximate entropy were calculated for all subjects. Result (1)EEG nonlinear indices of patient group were significantly lower than those of control group for all conditions and all brain regions. There was significant difference between the two groups (P＜0.05). (2)Under the auditory stimulus and painful stimulus states, all EEG nonlinear indices in the control group were higher than those under eyes-closed condition. Nonlinear indices in the patient group had almost no change for different conditions. Conclusion EEG nonlinear analysis may quantify the degree of unconsciousness in anoxia-ischemic patients. The changes of brain function for unconscious subjects could be captured by EEG nonlinear analysis. EEG nonlinear analysis could provide information about the outcome of unconscious anoxia-ischemic patients.