1. A method for detecting electrical defect of contact/via plugs, comprising: monitoring the contact/via plugs by an electron-beam (E-Beam) inspection tool to capture an image with a VC (voltage contrast) difference; performing an image extraction on the image with the VC difference, wherein the image extraction is based on target gray level/back ground gray level; contrasting the extracted image with a layout design base to obtain a blind contact or Quasi-blind issue of the contact/via plugs; and comparing a grayscale value of the VC difference having the blind contact or Quasi-blind issue with a predetermined range of grayscale value to determine whether the VC difference is abnormal.