  We study the Andreev reflection (AR) in a three terminal mesoscopic hybrid
system, in which two ferromagnets (F$_1$ and F$_2$) are coupled to a
superconductor (S) through a quantum dot (QD). By using non-equilibrium Green
function, we derive a general current formula which allows arbitrary spin
polarizations, magnetization orientations and bias voltages in F$_1$ and F$_2$.
The formula is applied to study both zero bias conductance and finite bias
current. The current conducted by crossed AR involving F$_1$, F$_2$ and S is
particularly unusual, in which an electron with spin $\sigma $ incident from
one of the ferromagnets picks up another electron with spin $\bar{\sigma}$ from
the other one, both enter S and form a Cooper pair. Several special cases are
investigated to reveal the properties of AR in this system.
