  The low braking-index pulsar PSR J1734$-$3333 could be born with superhigh
internal magnetic fields $B_{\rm in}\sim10^{15}-10^{16}$ G, and undergo a
supercritical accretion soon after its formation in a supernova explosion. The
buried multipole magnetic fields will merger into a dipole magnetic field.
Since the magnetic flow transfers from the core to the crust of the pulsar, its
surface dipole field grows quickly at a power-law form assumed until it
saturates at the level of internal dipole field. The increase in surface dipole
magnetic field results in the observed low braking index of $n=0.9(2)$. Keeping
an average field growth index $\varepsilon=1.34(6)$, this pulsar will become a
magnetar with surface dipole magnetic field at the equator $B_{\rm d}\sim
2.6(1)\times 10^{14}$\,G and $\sim 5.3(2)\times 10^{14}$\,G after next 50\,kyrs
and 100\,kys, respectively.
