In this paper,the Power Build-Up cavity enhanced Raman spectroscopy is introduced and the matching mode between the cavity length and wavelength is improved simultaneously.At the same time,the laser diode optical frequency modulation circuit is designed.Cavity length control system is built up to enhance the cavity power and experiments are also set up.The 532nm laser is coupled into an external linear optical cavity composed of two highly reflective mirrors.Since the light source is a solid laser,center light wavelength is a constant and line width is also known.