To improve the system capacity, the utilization rate of optical fiber and reduce the cost of network construction, this paper proposes a quantum and classical fusion communication system based on dense wavelength division multiplexing(DWDM) technology. To eliminate or reduce the impact of classical signal on quantum signal in the system, it designs an unequal wavelength allocation method and an optical isolator are to deal with the four wave mixing noise and Raman scattering noise of the fusion system respectively. The simulation results show that the quantum bit error rate(QBER) of the quantum and classical fusion communication system is reduced by 33.3% due to four wave mixing and Raman scattering noise after noise processing.