  We show that any bounded smooth helically symmetric solution $(\Bu, \Bh)$ in
$\mathbb{R}^3$ must be constant vectors. This is an extension of previous
result \cite[Theorem 1.1]{HWXAHE} from Navier-Stokes system to MHD system. The
proof relies on establishing a Saint-Venant type estimate to characterize the
growth of Dirichlet integral of nontrivial solutions.
