  In this paper we consider Abel equation $x' = g(t)x^2+f(t)x^3$, where $f$ and
$g$ are analytical functions. We proved that if the equation has a center at
$x=0$, then the Moment Conditions, i. e.,
$m_k=\int_{-1}^1f(t)(G(t))^kdt=0,~~k=0,1,2$, is satisfied where
$G(t)=\int_{-1}^tg(s)ds$. Besides, we give partial a positive answer to a
conjecture proposed by Y. Lijun and T. Yun in 2001.
