  The cumulant method is applied to study elliptic flow ($v_2$) in Au+Au
collisions at $\sqrt{s}=200$AGeV, with the UrQMD model. In this approach, the
true event plane is known and both the non-flow effects and event-by-event
spatial ($\epsilon$) and $v_2$ fluctuations exist. Qualitatively, the hierarchy
of $v_2$'s from two, four and six-particle cumulants is consistent with the
STAR data, however, the magnitude of $v_2$ in the UrQMD model is only 60% of
the data. We find that the four and six-particle cumulants are good measures of
the real elliptic flow over a wide range of centralities except for the most
central and very peripheral events. There the cumulant method is affected by
the $v_2$ fluctuations. In mid-central collisions, the four and six-particle
cumulants are shown to give a good estimation of the true differential $v_2$,
especially at large transverse momentum, where the two-particle cumulant method
is heavily affected by the non-flow effects.
