  We establish the well-posedness of the MHD boundary layer system in Gevrey
function space without any structural assumption. Compared to the classical
Prandtl equation, the loss of tangential derivative comes from both the
velocity and magnetic fields that are coupled with each other. By observing a
new type of cancellation mechanism in the system for overcoming the loss
derivative degeneracy, we show that the MHD boundary layer system is well-posed
with Gevrey index up to $3/2$ in both two and three dimensional spaces.
