Laser-to-ion energy conversion efficiency is important for ion-beam driven inertial confinement fusion. We propose to use a suitable plasma waveguide to enhance ion acceleration driven by an ultrashort ∼1021 W cm−2 laser pulse. Three-dimensional (3D) particle-in-cell (PIC) simulations show that, compared with that of the standard planar target, more than an order of magnitude increase of the maximum ion energy and energy conversion efficiency is possible. In particular, with a laser of intensity W cm−2, duration 26.7 fs and energy 0.85 J, 3D PIC simulations show that one can obtain 46 MeV protons and 150 MeV carbon ions, and ∼15% laser-to-ion energy conversion efficiency.