The low braking index pulsar PSR J1734-3333 could be born with a superhigh internal magnetic field of 10(14)-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 small braking index of n = 0.9. Keeping the current field-growth index E = 1.34, this pulsar will become a magnetar with surface dipole magnetic field at the equator B-d approximate to 2.6(1) x 10(14) G and approximate to 5.3(2) x 10(14) G after next 50 kyrs and 100 kys, respectively.