Since　heavy　vehicles　need　all-terrain　adaptability　and　large　load　drive　capability,　the　dual　hydraulic　cylinders　symmetrically　arranged　and　connected　in　series　are　widely　used　in　their　steering　system,　which　is　quite　different　from　the　traditional　electrohydraulic　power　steering　systems.　Accurate　steering　control　for　this　dual　hydraulic　system　is　challenged　due　to　its　complicated　structure　and　a　wide　range　of　steering　loads.　To　solve　this　issue,　an　improved　integral　sliding-mode　control　(ISMC)　is　presented　in　this　article.　Specifically,　a　hyperbolic　tangent　function　is　integrated　into　the　controller　to　mitigate　the　chattering　caused　by　the　sliding　mode.　A　stability　analysis　is　then　conducted　based　on　the　finite-time　Lyapunov　stability　theory,　revealing　the　proposed　controller＇s　capability　of　achieving　the　asymptotic　convergence　of　the　tracking　error　within　a　finite　time.　A　test　bench　is　also　established　to　experimentally　validate　the　controller＇s　effectiveness　through　multiple　test　scenarios,　including　various　tire　loads,　supply　pressures,　and　command　signals　frequencies.　The　results　show　that　the　tracking　error　of　ISMC　is　kept　within　0.5　degrees,　which　is　significantly　superior　to　PID　control.　In　addition,　the　ISMC　can　achieve　high-precision　control　under　lower　supply　pressure,　showing　the　energy-saving　potential　of　nonlinear　control　for　the　steering　system　in　heavy　vehicles.