The intra-day Optical Monitoring of BL Lacerate Object 1ES 1218+304 at
  Its Highest X-ray Flux Level
  We here report a monitor of the BL Lac object 1ES 1218+304 in both B- and
R-bands by the GWAC-F60A telescope in eight nights, when it was triggerd to be
at its highest X-ray flux in history by the VERITAS Observatory and Swift
follow-ups. Both ANOVA and $\chi^2$-test enable us to clearly reveal an
intra-day variability in optical wavelengths in seven out of the eight nights.
A bluer-when-brighter chromatic relationship has been clearly identified in
five out of the eight nights, which can be well explained by the shock-in-jet
model. In addtion, a quasi-periodic oscilation phenomenon in both bands could
be tentatively identified in the first night. A positive delay between the two
bands has been revealed in three out of the eight nights, and a negative one in
the other nights. The identfied minimum time delay enables us to estimate the
$M_{\mathrm{BH}}=2.8\times10^7 \rm M_{\odot}$that is invalid.
