This paper presents an automatic method to detect the position of 400.0 nm break in galaxies spectra. This spectral discontinuity is due to the opacity produced by the presence of a large number of spectral lines of ionized metal. It is largely used to determine the star formation characteristics of distant field and cluster galaxies. The position of the discontinuity is an indicator of redshift. Detecting the position by hand is not possible in a sky survey with large amount of spectra data. We develop an automatic method using wavelet transform and discrete convoution. All steps are given in the paper. The program subtracts the spectral lines from a continuum using wavelet filter and determines that the spectrum is an emission line galaxy. Then the discontinuity position is obtained by convolution between a step function and the continuum, at last, the program computes the redshift z, and identifies strong emission lines using computed z. When the strong lines are identified, the position is determined. We use 3 data set to test our program. The results suffice to show that discontinuity position is very precisely measured. This method can be the first step for studying the galaxies spectra surveys.