In the free-space quantum communication, the performance of communication systems has a great degradation due to the atmospheric effects, such as atmospheric absorption, scattering and turbulence. However, quantum signals with different wavelengths is differently affected by atmospheric characteristics. In this paper, in order to investigate the effects of different wavelengths quantum signals on free-space quantum key distribution, an entanglement-based continuous variable quantum key distribution transmission model is established. Considering the influence of various atmospheric effects on quantum signals, the secret key generation rates are calculated though the homodyne detectors. The simulation results show that the long-wavelength signal can enhance the secret key generation rates at the same transmission distance. Therefore, the long-wavelength signal is more suitable for the free-space quantum transmission.