  The magnetotransport properties of disordered ferromagnetic Weyl semimetals
are investigated numerically. We found an extraordinarily stable and huge
magnetoresistance effect in domain walls of Weyl semimetals. This effect
originates from the helicity mismatch of Weyl fermions and is a specific
property of Weyl semimetals. Although conventional magnetoresistance effects
are strongly suppressed in domain walls where local magnetization varies
gradually, the helicity-protected magnetoresistance in Weyl semimetals
maintains almost $100\%$ of the magnetoresistance ratio for any kind of thick
domain walls, even in the presence of disorder. The contribution of surface
Fermi arcs to the magnetoresistance is also discussed.
