  The nonlinear dynamo effect of tearing modes is derived with the resistive
MHD equations. The dynamo effect is divided into two parts, parallel and
perpendicular to the magnetic field. Firstly, the force-free plasma is
considered. It is found that the parallel dynamo effect drives opposite current
densities at the different sides of the rational surface, making the $\lambda
=\boldsymbol{j}\cdot\boldsymbol{B}/|\boldsymbol{B}|^2$ profile completely
flattened near the rational surface. There are many rational surfaces for the
turbulent plasma, which means the plasma is tending to relax into the Taylor
state. In contrast, a bit far from the rational surface, the parallel dynamo
effect is much smaller, and the nonlinear dynamo form approximates the
quasilinear form. Secondly, the pressure gradient is included. It is found that
rather than the $\lambda$ profile, the $\boldsymbol{j}\cdot\boldsymbol{B}$
profile is flattened by the parallel dynamo effect. Besides, the perpendicular
dynamo effect of tearing modes is found to eliminate the pressure gradient near
the rational surface. In addition, our result also provides another basis for
the assumption that current density is flat in the magnetic island for the
tearing modes theory.
