  The 9.7$\mu m$ and 18$\mu m$ interstellar spectral features, arising from the
Si--O stretching and O--Si--O bending mode of amorphous silicate dust, are the
strongest extinction feature in the infrared. Here we use the "pair method" to
determine the silicate extinction profile by comparing the \emph{Spitzer}/IRS
spectra of 49 target stars with obvious extinction with that of un-reddened
star of the same spectral type. The 9.7$\mu m$ extinction profile is determined
from all the 49 stars and the 18$\mu m$ profile is determined from six stars.
It is found that the profile has the peak wavelength around $\sim$9.2- 9.8$\mu
m$ and $\sim$18-22$\mu m$ respectively. The peak wavelength of the 9.7$\mu m$
feature seems to become shorter from the stars of late spectral type, meanwhile
the FWHM seems irrelevant to the spectral type, which may be related to
circumstellar silicate emission. The silicate optical depth at 9.7$\mu m$,
$\Delta\tau_{9.7}$, mostly increases with the color excess in $J-K_S$ ($E_{\rm
JK_S}$). The mean ratio of the visual extinction to the 9.7$\mu m$ silicate
absorption optical depth is $A_{\rm V}/\Delta\tau_{9.7}\approx 17.8$, in close
agreement with that of the solar neighborhood diffuse ISM. When $E_{\rm JK_S}$
> 4, this proportionality changes. The correlation coefficient between the peak
wavelength and FWHM of the 9.7$\mu m$ feature is 0.4, which indicates a
positive correlation considering the uncertainties of the parameters. The
method is compared with replacing the reference star by an atmospheric model
SED and no significant difference is present.
