Abstract: Some common characters in the video information leaked by a computers system are the texture characteristics which are composed of moving black areas of a reconstructed image from the leaked video information. The texture characteristics are quite different with the varying of synchronal frequency. The moving speed of the texture increases when the synchronal error becomes larger. And the moving direction is decided by the sign of the error. According to these features, a similar Harr Wavelet method is used to extract the synchronal characters in the video information leaked by a computer system. Based on these synchronal characters, the angles tilted by the synchronal error are used to adjust the frequency of the synchronal pulses until the synchronal accuracy is enough for steady display.