Potassium ion batteries (KIB) have been considered as helpful alternative energy storage devices owing to the low-cost and abundant potassium sources. However, it is a critical challenge to explore suitable anode materials and electrolytes for adapting large radius and high activity of K ions. In this study, a novel FeSe2 nanoparticle embedded in 3D honeycomb-like N-doped carbon architectures (FeSe2-NC) is synthesized through a simple solid-state strategy. Such unique architecture structure can not only provide a high-way for electron and K+ transport, but also effectively alleviate volume variation during long-term K+ intercalation/deintercalation process. Hence, FeSe2-NC as anode materials for KIB display a high discharge capacity of 460 mAh g−1 at 100 mA g−1 and excellent long-term cycling stability even at a high current density of 2 A g−1. Beyond the electrochemical performance, it is found that storage K+ of FeSe2-NC represents a conversion mechanism during discharge/charge in KIB. Furthermore, regulating the electrolyte salts via replacing potassium bis(fluorosulfonyl)imide (KFSI) electrolyte with potassium hexafluorophosphate (KPF6) electrolyte can form a more uniform and robust solid electrolyte interphase film, which be responsible for the enhanced electrochemical performance. Therefore, it is helpful to understand the fundamentals of FeSe2-NC and promote the practical application of KIB.