Aim: To probe into the feature of cerebral admittance plethysomgraphy, and study cerebrovascular functional state. Methods: We recruited 30 patients with hypertension and arteriosclerosis respectively who received treatment in Department of Neurology, Xuanwu Hospital, Capital University of Medical Sciences from September 2004 to January 2005. Another 30 healthy persons were chosen from Capital University of Medical Sciences between September 2002 and January 2003. 1 Forehead-mamillary process of brain asmittance of the subjects in each group was given lead detection with ENG bilateral admittance rheo-encephalogram automatic detection. The wavelet pack technology was used to extract different frequencies of entropy feature of brain admittance to perform comparison and statistical analysis. Results: Thirty patients respectively in the two groups and 30 healthy persons in normal control group entered the stage of result analysis. 1 2-grade decomposition of wavelet pack showed that the entroy value was both lower in hypertension group and arteriosclerosis group than in normal control group. There was significant difference of T (2,1)entroy feature value between hypertension group and arteriosclerosis group (303.61±20.48, 368.09±14.20,P=0.012). 2 3-grade decomposition showed that there was significant difference of entroy feature value at middle-frequency between hypertension group and normal control group T(3,1),T(3,2) and T(3,4) (P < 0.05); The entroy feature in the arteriosclerosis group all had significant meaning. Conclusion: There is difference of entroy feature value extracted from brain admittance with wavelet packet technique between normal control group and abnormal group. Moreover, the difference at middle-frequency is significant. Decomposition of brain admittance and study of cerebral function state with wavelet package analysis technology will provide basis for further study such as signal classification.