The research and development of potassium ion battery (KIB) is still currently at infancy stage due to the lack of materials that facilitate rapid K+ transport and subsequently deliver high energy capacity and power density. Our Density Functional Theory (DFT) calculations suggest that the high potassium adsorption energy (3.01 eV) on 1D-C3N4, a lower potassium diffusion barrier and the superior electronic conductivity of graphene will be beneficial for the intercalation of K+. In this work, a 1D/2D C3N4/reduced graphene oxide (rGO) composite was designed and synthesized as an anode material to address these needs via a hydrothermal/freeze drying method. As a host for K+ ions, the as prepared composite delivered a remarkable specific capacity of 464.9 mAh/g after 200 cycles at 1 A/g and 228.6 mAh/g after 1000 cycles at 10 A/g, which is one of the best reported so far. The exceptional performance of this composite can be attributed to the large surface area for additional active sites, shorter K+ diffusion distance, structural stability and the synergistic interaction between 1D C3N4 and 2D rGO. This work broadens the design and application of composites and fosters the advancement in potassium ion battery research.