In this paper, we numerically study the magnetic transport properties of disordered Weyl semimetals (WSM) in the ultraquantum limit. We find a positive magnetic conductivity for the long-range disorder, although the system tends to have negative magnetic conductivity for the weak short-range disorder. Remarkably, for long-range disorder, such a positive magnetic conductivity usually cannot be described by the semiclassical Boltzmann transport theory even in the weak disorder limit, and the backscattering assisted by the high Landau levels is always important. Our results have significant implications for the positive magnetic conductivity recently discovered in the WSM systems, and point out two physical mechanisms: (i) the long-range correlated disorder suppresses the backscattering among the zeroth Landau level modes; (ii) with increasing the magnetic field, the backscattering assisted by the high Landau levels will also be suppressed.