Abstract: As a research tool of the turbulent flow, spectrumanalysis can decompose the complex flow into the flows with the variousscales. By DNS data, the spectra of fluctuant kinetic energy, velocityand temperature are analyzed in turbulent flow of natural convectionbetween two infinite vertical differently heated walls. Results showthat the ranges of all these spectra are very broad from the largest tothe smallest scales, time step is small enough to be used in DNS. Fromthe energy distribution, energy region, inertial sub-region anddissipation region can been observed, the characteristics of theseregions are concluded. Due to the high anisotropy of this kind of theturbulent flow, inertial sub-region is much small. Further, theinfluence of the vertical position to the fluctuant kinetic energy andto the energy spectrum is discussed, the characteristic of large-scalestructures in the frequency space is showed also in the paper.