  The spin down behaviors of SGR 0418+5729 are investigated. The pulsar spin
down model of Contopoulos & Spitkovsky (2006) is applied to SGR 0418+5729. It
is shown that SGR 0418+5729 lies below the pulsar death line and its
rotation-powered magnetospheric activities may therefore have stopped. The
compact star is now spun down by the magnetic dipole moment perpendicular to
its rotation axis. Our calculations show that under these assumption there is
the possibility of SGR 0418+5729 having a strong dipole magnetic field, if
there is a small magnetic inclination angle. Its dipole magnetic field may be
much higher than the characteristic magnetic field. Therefore, SGR 0418+5729
may be a normal magnetar instead of a low magnetic field magnetar.
