  So far quite a few ultraluminous X-ray (ULX) pulsars have been discovered. In
this work, we construct a super-Eddington, magnetic accretion disk model to
estimate the dipole magnetic field of eight ULX pulsars based on their observed
spin-up variations and luminosities. We obtain two branches of dipole magnetic
field solutions. They are distributed in the range of $B\sim (0.16-64.5)\times
10^{10}\,{\rm G}$ and $\sim (0.275-79.0)\times 10^{13}\,{\rm G}$ corresponding
to the low- and high-$B$ solutions respectively. The low magnetic field
solutions correspond to the state that the neutron stars are far away from the
spin equilibrium, and the high magnetic field solutions are close to the spin
equilibrium. The ultra-strong magnetic fields derived in Be-type ULX pulsars
imply that the accretion mode in Be-type ULX pulsars could be more complicated
than in the persistent ULX pulsars and may not be accounted for by the
magnetized accretion disk model. We suggest that the transition between the
accretor and the propeller regimes may be used to distinguish between the low-
and high-$B$ magnetic field solutions in addition to the detection of the
cyclotron resonance scattering features.
