In the present paper the author offers a method to search the QSO candidates and calculate their redshfit using their broad emission lines which are the most important character of quasars. It is hard to identify the lines in the quasar’s spectra due to their redshifts distributing on a broad range. Spectra contain two components. One is continuum and the other is lines. The author uses a method of LFPS (low frequency points set) to build the continuum and detect the obvious emission lines, a method that can avoid the broad emission lines as a part of the continuum. The redshift can be calculated by comparing the extracted lines with the line table. The classification can be done with both emission lines and the redshift. For a better accurate rate to recognize the lines, this paper provides a method to estimate the level of the local noise. The method this paper used is independent of the flux calibration of the spectra. It can work for the spectra of the present LAMOST.