  Recent simulation and experimental results suggest that the magnetic island
and flow on resonant surface often do not satisfy the "no-slip" condition in
the steady state. A new theory model on nonlinear plasma response to external
magnetic perturbation in absence of no-slip condition is proposed. The model is
composed of the equations for the evolution of both width and phase of magnetic
island due to forced reconnection driven by the external magnetic perturbation,
and the force-balance equation for the plasma flow. When the island width is
much less than the resistive layer width, the island growth is governed by the
linear Hahm-Kulsrud-Taylor solution in presence of time-dependent plasma flow.
In the other regime when the island width is much larger than the resistive
layer width, the evolution of both island width and phase can be described
using the Rutherford theory. The island solution is used to construct the
quasi-linear electromagnetic force, which together with viscous one,
contributes to the nonlinear variation in plasma flow. The no-slip condition
assumed in the conventional error field theory is not imposed here, where the
island oscillation frequency depends on but does not necessarily equal to the
plasma flow frequency at the rational surface.
