Abstract: The paper introduce a method that repairig high voltage malfunction of SHIMADZU SCT-3000TE. That indicate KV ripple affect obviously mA value, the more X-ray photon number, the stronger of accepted signal, but the more KV ripple, the more low energy photon, the less high energy photon, the less photon that arrived at the detector. When malfunction has happened, although the KV average value is normal, but the range of KV ripple change 60%, out of tolerance (less than 10%), so the photon that detected is too low, debase the image quality.