High-pressure effect on the properties of onion was investigated. The dielectric properties of high-pressure treated onion were measured at 50 Hz- 5 MHz. Radius of Cole-Cole arcs of high-pressure treated samples were smaller than untreated. Radius of treated onion completely disappeared at 400 MPa. This indicated that cell structure would be damaged by high-pressure treatment. Next influences of high-pressure treatment on functional properties were analyzed. Antioxidative activities of high-pressure treated onion at 200 or 400 MPa were increased during storage at 25℃. The constituents of high-pressure treated onion were analyzed by HPLC. Scatter plot between high-pressure treated and untreated peak area ratio (sample peak area/internal standard peak area) were analyzed. Area ratios of untreated samples were plotted on x-axis and those of high-pressure treated were on y-axis according to the retention time. The slope with the retention time of 27.3 min was over 1.0. This indicated that the slope over 1.0 was positive-affected by high-pressure treatment. The ingredient with the retention time of 27.3 min was identified as quercetin. Scatter plot was a novel tool to extract the high-pressure effected substances from multiple and unidentified data. These changes of structural and functional properties of foodstuffs are defined as “High-Pressure Induced Transformation (Hi-Pit).”