Abstract: Due to urgent requirement for high speed transmission, digital atmospheric laser communication system based on double channel dense wavelength division multiplexing (DWDM) is experimentally demonstrated. Optical carriers are provided by two lasers at 1539.76 nm and 1540.55 nm respectively, and intensity modulation is adopted. After being multiplexed and amplified, DWDM signals are transmitted through an optical antenna. Spectrums, waveforms and eye diagrams are measured at receiver after transmission in the atmosphere via 1km. Experimental results show that DWDM signals are de-multiplexed in weak turbulence, and waveforms and eye diagrams are observed clearly. The Q-factors are more than 5 when transmitting 20 Gbit/s modulated signals simultaneously.