  In a sample of 60 quasars selected from Sloan Digital Sky Survey (SDSS) with
at least six-epoch spectroscopy, we investigate the variability of emission
lines and continuum luminosity at various aspects. A strong anti-correlation
between the variability and continuum luminosity at 2500 {\AA} is found for the
sample, which is consistent with previous works. In individual sources, we find
that half of the sample objects have a trend of being bluer-when-brighter trend
(BWB), while the remaining half exhibit redder-when-brighter trend (RWB).
Although the mechanism for RWB is unclear, the effects of host galaxy
contribution due to seeing variations can not be completely ruled out. As
expected from photoionization model, the positive correlations between the
broad emission line and continuum luminosity are found in most individual
sources, as well as for the whole sample. We confirm the Baldwin effect in most
individual objects and the whole sample, while a negative Baldwin effect is
also found in several quasars, which can be at least partly (if not all) due to
the host galaxy contamination. We find positive correlations between the broad
emission line luminosity and line width in most individual quasars, as well as
the whole sample, implying a more variable line base than the line core.
