An equipment for collectively monitoring the wavelength in DWDM system and a method thereof, the said equipment for collectively monitoring the wavelength comprises a plurality of light emitter for emitting the optical signals with different wavelengths; a wave synthesizer for multiplexing the optical signals as an optical multiplex signal and transmitting the light multiplex signal; a power sampler for getting a light multiplex sample signal from the light multiplex signal; a variable band-pass filter for receiving the light multiplex sample signal, and sequentially selecting an optical signal output with different wavelengths from the light multiplex sample signal; a broadband wavelength locker for detecting the wavelength offset of optical signal from the variable band-pass filter; a signal processor for calculating the amount of compensate control according to the wavelength offset; and a controler for controlling the light emitter to adjust the wavelength according to the amount of compensate control. The present invention has simple construction and method, lower system cost and facilicates the system to expand a capacity smoothly, and greatly fits for the high capacity DWDMsystem with a channel interval of 50G and less.