We investigate the Dirichlet problem associated to the Schrödinger operator \(\mathcal {L}=-\Delta _{\mathbb {H}^n} + V\) on Heisenberg group \(\mathbb H^n\) : \(\begin{aligned} {\left\{ \begin{array}{ll} \partial _{ss}u(g,s)-\mathcal {L}u(g,s) = 0\,,\quad & \mathrm{in \,\ } \mathbb {H}^n\times \mathbb {R}^+,\\ u(g,0) = f \,,\quad & \mathrm{on \,\ } \mathbb {H}^n \end{array}\right. } \end{aligned}\) with f in \(L^p(\mathbb {H}^n)\) ( \(1< p<\infty \) ) and in \(H^1_{\mathcal {L}}(\mathbb {H}^n)\) , i.e., the Hardy space associated with \(\mathcal {L}\) . Here \(\Delta _{\mathbb {H}^n}\) is the sub-Laplacian on \(\mathbb H^n\) and the nonnegative potential V belongs to the reverse Hölder class \(B_{Q/2}\) with Q the homogeneous dimension of \(\mathbb {H}^n\) . The new approach is to establish a suitable weak maximum principle, which is the key to solve this problem under the condition \(V\in B_{Q/2}\) . This result is new even back to \(\mathbb R^n\) (the condition will become \(V\in B_{n/2}\) ) since the previous known result requires \(V\in B_{(n+1)/2}\) which went through a Liouville type theorem.