  We made model fitting to the mid-to-far infrared spectral energy
distributions (SEDs) for different categories of galaxies in the main
extragalactic field of the {\it Spitzer} First Look Survey with the aid of
spectroscopic information from the Sloan Digital Sky Survey. We find that the
mid-to-far infrared SEDs of HII galaxies, mixture type galaxies and LINERs can
be well fitted by the one-parameter ($\alpha$) dust model of Dale et al. plus
the 13 Gyr dust-free elliptical galaxy model. The statistics of $\alpha$ values
indicates that all these galaxies tend to be quiescent, although the HII
galaxies are relatively more active than the LINERs. The mid-infrared SEDs of
absorption galaxies are well fitted simply by the 13 Gyr dust-free elliptical
galaxy template, and the near-to-mid infrared SEDs of QSOs can be represented
by AGN NGC 5506.
