<p>Recent achievements have demonstrated that carbon nanotubes (CNTs) and graphene can support surface plasmons (SPs), however, the plasmon modes in mixed-dimensional heterostructures based on graphene and CNTs remain less explored. This study proposes a mixed-dimensional van der Waals heterostructure based on the CNTs and graphene layer, which exploits the coupling between single-walled/double-walled carbon nanotubes (SW/DWCNTs) and graphene to excite the H₁ hybrid mode and the CM₁ and CM₂ coupled modes, respectively, achieving a group velocity as low as 10^− 3<i>c</i>, an order of magnitude lower than that of intrinsic graphene plasmons. In particular, the CM₂ mode in the double-walled structure exhibits an effective refractive index as high as 387, strong field localization with normalized mode field areas of ~ 10^− 7, low-loss transmission with <i>L</i>_P/<i>λ</i>_SP around 14, and good temperature stability. These findings provide theoretical guidance for the development of tunable plasmonic devices through dimensional engineering and offer a high-performance material platform for mid-infrared integrated photonic devices.</p>