It is difficult to obtain the wide band spectrum of the target in the hard target detection with strong background weak signal by laser. A single spectral peak recognition method based on brewster angle is proposed. By combining the characteristics of pPolarized reflectivity and characteristics of typical target extinction coefficient, the brewster angle solution of hard target is obtained by extremum finding by the second derivative in the hard target detection model. The results show that the brewster angle of nonmetallic hard targets is correlated with inverse triangulation of double index. Therefore, the single spectral peak method can be used to identify the target material by means of the laser which covers the peak spectral segment of the target refractive index.