  The Weyl semimetal (WSM) is a novel topological gapless state with promises
exotic transport due to chiral anomaly. Recently, a family of nonmagnetic WSM
candidates including TaAs, NbAs, NbP etc is confirmed by first principle
calculation and experiments. The TaAs family are reported to display the large
unsaturated magnetoresistance (XMR), which have not yet been explained. Here,
we give a theoretical calculation of XMR based on the extended effective-medium
approach to Weyl semimetals. We predict the power law of XMR at high magnetic
field and the "turn-on" magnetic field, which are well in agreement with
experiments data. Furthermore, we investigate the $\theta$-dependence
magnetoresistance and find the transition between the postive XMR and the
negative magnetoresistance induced by chiral anomaly, which should be confirmed
by further experiments.
