  We analyze X-ray spectra of 43 Palomar-Green quasars observed with {\it
XMM-Newton} in order to investigate their mean Fe K line profile and its
dependence on physical properties. The continuum spectra of 39 objects are well
reproduced by a model consisting of a power law and a blackbody modified by
Galactic absorption. The spectra of the remaining four objects require an
additional power-law component absorbed with a column density of $\sim 10^{23}
{\rm cm}^{-2}$. We fit the entire sample simultaneously to derive average Fe
line parameters by assuming a common Fe line shape. The Fe line is relatively
narrow ($\sigma=0.36$ keV), with a center energy of 6.48 keV and a mean
equivalent width (EW) of 248 eV. By combining black hole masses estimated from
the virial method and bolometric luminosities derived from full spectral energy
distributions, we examine the dependence of the Fe K line profile on Eddington
ratio. As the Eddington ratio increases, the line becomes systematically
stronger (EW = 130 to 280 eV), broader ($\sigma=0.1$ to 0.7 keV), and peaks at
higher energies (6.4 to 6.8 keV). This result suggests that the accretion rate
onto the black hole directly influences the geometrical structure and
ionization state of the accretion disk.
