In this investigation 50 normal subjects were observed. Activities of EEG of 8 areas on both hemisphere during six different states were recorded. The author analyzed time ( T ), area( A ) and amplitude ( Amp ) of burst 40 Hz ERP recorded during different states and investigate the correlation's between 40 Hz ERP and age, sex,education background and scores of IQ. The time, area and amplitude of burst 40 Hz ERP are all significantly lower during rest states than those during orientation test, calculation test and visual spatial task test. During thinking process the increase of burst 40 Hz ERP is positive correlated with the scores in MMSE and WAIS. T is the most stable and sensitive marker. A affected by T and Amp, is stable but less sensitive than T. Amp is less sensitive than T and A.