  The attenuation of high-energy gamma-ray spectrum due to the
electron-positron pair production against the extragalactic background light
(EBL) provides an indirect method to measure the EBL of the universe. We use
the measurements of the absorption features of the gamma-rays from blazars as
seen by Fermi Gamma-ray Space Telescope to explore the EBL flux density and
constrain the EBL spectrum, star formation rate density (SFRD) and photon
escape fraction from galaxies out to z=6. Our results are basically consistent
with the existing determinations of the quantities. We find a larger photon
escape fraction at high redshifts, especially at z=3, compared to the result
from the recent Ly-alpha measurements. Our SFRD result is consistent with the
data from both gamma-ray burst and UV observations in 1-sigma level. However,
the average SFRD we obtain at z>~3 matches the gamma-ray data better than the
UV data. Thus our SFRD result at z>~6 favors that it is sufficiently high
enough to reionize the universe.
