  Twenty-one new optical light curves, including five curves obtained in 2009
and sixteen curves detected from the AAVSO International Database spanning from
1977 to 2011, demonstrate 16 new primary minimum light times in the high state.
Furthermore, seven newly found low-state transient events from 2006 to 2009
were discovered, consisting of five Gaussian-shaped events and two events with
an exponential form with decay timescales of $<$0.005 days; these timescales
are one order of magnitude shorter than those of previous X-ray flare events.
In the state transition, two special events were detected: a "disrupted event"
with an amplitude of $\sim$ 2 mag and a duration of $\sim$ 72 minutes and
continuing R-band twin events larger than all known R-band flares detected in
M-type red dwarfs. All 45 available high-state data points spanning over 35 yr
were used to construct an updated O-C diagram of \objectname{AM Herculis},
which clearly shows a significant sine-like variation with a period of 12-15 yr
and an amplitude of 6-9 minutes. Using the inspected physical parameters of the
donor star, the secular variation in the O-C diagram cannot be interpreted by
any decided angular momentum loss mechanism, but can satisfy the condition
$\tau_{\dot{\rm M}_{2}}\simeq\tau_{\rm KH}>>\tau_{\dot{\rm R}_{\rm 2}}$, which
is required by numerical calculations of the secular evolution of cataclysmic
variables. In order to explain the prominent periodic modulation, three
plausible mechanisms - spot motion, the light travel-time effect, and magnetic
active cycles - are discussed in detail.
