  Under the hypothesis of gravitational redshift induced by the central
supermassive black hole, and based on line widths and shifts of redward shifted
H$\beta$ and H$\alpha$ broad emission lines for more than 8000 SDSS DR7 AGNs,
we measure the virial factor in determining supermassive black hole masses. The
virial factor had been believed to be independent of accretion radiation
pressure on gas clouds in broad-line region (BLR), and only dependent on
inclination effects of BLR. The virial factor measured spans a very large
range. For the vast majority of AGNs ($>$96%) in our samples, the virial factor
is larger than $f=1$ usually used in literatures. The $f$ correction makes the
percent of high-accreting AGNs decrease by about 100 times. There are positive
correlations of $f$ with the dimensionless accretion rate and Eddington ratio.
The redward shifts of H$\beta$ and H$\alpha$ are mainly the gravitational
origin, confirmed by a negative correlation between the redward shift and the
dimensionless radius of BLR. Our results show that radiation pressure force is
a significant contributor to the measured virial factor, containing the
inclination effects of BLR. The usually used values of $f$ should be corrected
for high-accreting AGNs, especially high redshift quasars. The $f$ correction
increases their masses by one--two orders of magnitude, which will make it more
challenging to explain the formation and growth of supermassive black holes at
high redshifts.
