In conventional analysis of electrogastrogram (EGG), the time percentage of normal slow waves is used to assess the regularity of the slow waves. A new parameter termed relative power percentage of normal slow waves is proposed in this paper to assess the regularity of slow waves from the view of power. Furthermore, the time and relative power percentage are conjoined in the Time-Power percentage map to analysis EGG slow waves. The new method is applied in the study of acupuncture regulation gastric function, and the result shows that both duration and amplitude are regulated under and after electroacupuncture. That may give illumination to mechanism study of acupuncture.