Potassium ion hybrid capacitors (KIHCs) have drawn growing interest owing to their outstanding energy density, power density and excellent cycling stability. However, the large ionic radius of potassium triggers a huge volume change during continuous K+ insertion/extraction processes, restricting the development of KIHCs. Here, we report N-doped carbon nanotubes (NCNTs) for high-performance K+ storage. The NCNTs possess a hierarchical structure and N functional groups and not only offer sufficient space to relieve the volume expansion, but also provide highly efficient channels to transport electrons and ions. As a result, the NCNTs anode presents a high specific capacity and an excellent cycling stability with an average decay rate of 0.0238% per cycle (the lowest value among the reported carbon-based anodes for K-ions batteries) during 3600 continuous cycles. A potassium ion hybrid capacitor (KIHC) was also designed with the NCNT anode and a commercial active carbon cathode and achieved both a high energy/power density (117.1 W h kg-1/1713.4 W kg-1) and a long cycle life (2000 cycles at 1 A g-1). Moreover, the in situ Raman and ex situ element mapping characterization demonstrate the outstanding electrochemical reversibility of the NCNTs. This work provides a superior strategy to design low-cost anode materials with excellent K+ storage electrochemistry.