Abstract: The electroencephalographic(EEG) changes in 8 volunteers after infusion of 15 mg midazolam were analysed quantitatively with the computer EEG analysis hardware and software made by authors. The changes of the total number of waves per second and total voltage per second following in 1～3,4～7,8～11 and 12～30 Hz frequency bands derived from aperiodic analysis were compared with those of tracing EEG. The results showed that the total number of waves per second following in 12～30 Hz band had the characteristic of being an ideal pharmacological indicator. The success of finding such a parameter reflecting the EEG effect makes it possible to study the concentration-effect relationship of midazolam.