In this paper, direct numerical simulations (DNS) have been performed to investigate the superimposition and modulation effects of Taylor-Gortler (TG) vortices on near-wall coherent structures in the context of streamwise-rotating turbulent channel flow. The evolution and dynamic interaction of the TG vortices with near-wall streaks have been studied in both spectral and physical spaces. An interesting bimodal pattern is observed in the pre-multiplied energy spectra which effectively differentiates the characteristic length scales of near-wall streaks from those of TG vortices. In the physical space, it is discovered that the near-wall streaks are influenced by the superimposition effect of TG vortices, and vary quasi-periodically in the spanwise direction. It is also interesting to observe that with positive and negative superimposition effects of TG vortices, the intensity of streaks is enhanced and reduced, respectively, clearly revealing that TG vortices has an amplitude-modulation effect on the near-wall structures.