  We propose a $U(1)'$ model from $E_6$ which has an isospin-violation dark
matter. By choosing a proper linear combination of two extra $U(1)$ gauge
symmetries in $E_6$, it is natural to realize the ratio $f_n/f_p=-0.7$ so as to
maximally relax the constraints from the Xenon based direct detection
experiments. We study the sensitivities of the dark matter direct and indirect
detection experiments, and identify the parameter spaces that can give the
observed relic density. We also study the sensitivities of the future colliders
with center mass energy $\sqrt{s}$= 33/50/100 TeV, and compare the different
detection methods. We show that in some parameter spaces the future colliders
can give much stronger limits.
