In this paper, new parameters were developed to estimate the depth of anesthesia during a general anesthesia using EEG. Power spectral density(PSD) analysis was used for these parameters because EEG became slow wave during anesthesia. The new parameters were DTR, ATR, TDR, ADR, BTR and BDR applied to PSD. These parameters were compared with SEF which is conventionally used at clinic and confirmed clinical value. As the results, DTR, ATR, TDR, ADR among parameters were not useful compared with SEF but BTR and BDR is valuable for clinic. 15 patents, at pre-operation BDR the value is $265.36{pm}25.29$, at induction the value is $129.23{pm}34.92$, at operation the value is $154.99{pm}38.34$, at awaked the value is $283.83{pm}39.80$ and at post-operation the value is $234.80{pm}23.46$. Also at pre-operation BTR value is $183.38{pm}13.59$, at induction the value is $104.09{pm}25.11$, at operation the value is $115.38{pm}23.42$, at awaked the value is $190.33{pm}23.31$ and at post-operation the value is $172.38{pm}19.08$. Trend of BDR and BTR is similar to change of SEF, so two parameters are useful. to estimate the depth of anesthesia.