  In this proceedings, we present STAR's measurement of $v_{2}$ difference
between positively charged pions and negatively charged pions at low transverse
momentum for Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The integrated
$v_2$ of $\pi^+$ ($\pi^-$), $0.15 < p_T < 0.5 GeV/c$, decreases (increases)
linearly with the increasing charge asymmetry $A_{\pm}$. The $v_2$ difference
between $\pi^+$ and $\pi^-$ is proportional to $A_{\pm}$ and the slope
parameters have their order of magnitude of about 0.01. All of these observed
features are consistent with the predication based on Chiral Magnetic Wave. The
centrality dependence of the $v_2$ difference is different than that was
predicted.
