Conducting quantum key distribution (QKD) through existing optical fibers together with conventional communication signals is a viable way to expand its practical application, but weak quantum signals can be severely disrupted by co-propagating classical signals. In this paper, the suppression of four-wave mixing (FWM) noise and Raman noise is considered simultaneously for the first time, to the best of our knowledge, and the joint optimized channel allocation (JOCA) scheme is proposed. In the JOCA scheme, the quantum channels and classical channels are interleaved with each other to avoid FWM noise and optimal quantum channel positions are chosen in variable conditions according to the Raman scattering spectrum. Experimental measurements of the noise photons show that the JOCA scheme can effectively reduce the impairments on quantum signals compared with the single-target schemes. Additionally, simulation results verify that the JOCA scheme can increase the secure key generation rate and transmission distance, and that it also enables the DWDM-QKD system to tolerate higher-power classical signals and more classical channels, which improve the compatibility with a high-capacity communication system.