The molecular gas in the host galaxies of the quasars at high redshift reveals key aspects in the formation and evolution of the SMBHs and their hosts at the early evolutionary stage. The CO spectral energy distributions (SLEDs) serve as powerful diagnostics of the physical conditions as well as heating mechanisms of the molecular gas, e.g., the photo-dissociation regions (PDRs), and the X-ray dominated regions (XDRs) heated by the star formation and the active galactic nucleus (AGN), respectively. In this talk, I will present our recent NOEMA observations of the CO, H2O, and dust continuum emissions in two quasars at z~6. I will analyze the dust properties using a general opacity dust SED model. By comparing the CO SLEDs with radiative transfer models and other galaxies at different redshifts, I will discuss the physical conditions as well as the heating mechanisms of the molecular gas in these two quasars at z~6.