Potassium-ion batteries (PIBs) have economic and environmental potential, but slow potassium ion diffusion and electrode material degradation hinder the development of effective cathode materials. This research designs a composite cathode material that vanadium disulfide with sulfur vacancies integrated with reduced graphene oxide (VS2-x@rGO). The introduction of sulfur vacancies increases active sites for ion storage, while rGO ensures a stable electronic conductivity and structural integrity. VS2-x@rGO shows a great rate performance of 116.2 mAh g−1 at 20 mA g−1, 77.5 mAh g−1 at 500 mA g−1, and high cycling stability with 94.5 % retention of capacity after 100 cycles at 100 mA g−1. Moreover, the full cell assembled with hard carbon achieves a specific capacity close to 120 mAh g−1. Energy density up to 220 Wh kg−1 in 38.4 W kg−1 and 72 Wh kg−1 in 960 W kg−1. Through in-situ XRD and other ex-situ analyses, the crystal structure rapidly transformed into K0.6VS2 and slight displacement of the crystal plane occurred during K+ insertion until KxVS2 formed in the discharge process. The charging process is reversible and forms VS2. This study provides a novel approach for advancing PIBs cathode materials, contributing valuable insights into the optimization of energy storage solutions.