As a typical layered transition metal chalcogenide, VS4 is considered as a promising cathode material for advanced magnesium-ion batteries. However, the poor electronic conductivity and severe polarization effect restrict its practical applications. Herein, we report a betaine-assisted solvothermal strategy to coat VS4 nanoblocks on the surface of carbon nanotubes (CNTs), obtaining unique core-shell-structured CNT@VS4 nanonecklaces. As a result of the morphology-controlling effect of betaine, VS4 exhibits an unusual nanoblock morphology, which renders abundant active sites and promotes the contact between the electrode and electrolyte. CNTs serve as a highly conductive skeleton, combining with the VS4 nanoblocks and ensuring their uniform distribution. As a benefit from the synergistic effect of abundant active sites and electron-conductive highways, the as-synthesized CNT@VS4 nanonecklaces manifest remarkable performance for magnesium storage, including a large reversible capacity of 170 mAh g-1 at 0.1 A g-1, outstanding cycle stability (76.3 mAh g-1 after 800 cycles at 0.5 A g-1), and superior rate performance (77.2 mAh g-1 at 2 A g-1).