Nitrogen-doped porous carbon nanoparticle (NPCN) was obtained by pyrolyzing nitrogen containing conjugated microporous polymer (NCMP). KOH high temperature activation following HNO3 neutralizing was also employed to acquire NPCN-KOH with improved porous structure. NPCN and NPCN-KOH were characterized by SEM, TEM, XPS, Raman spectroscopy, BET, cyclic voltammetry and charge-discharge test. SEM results indicate that both NPCN and NPCN-KOH are nanoparticles with a size about 100 nm. TEM results imply that KOH activation promotes the catalyst granules fusing together to form large particles in NPCN-KOH. XPS and elemental analysis indicate HNO3 neutralizing can increase the nitrogen content. Raman spectroscopy indicate NPCN-KOH possess more disordered structure. BET analysis reveals that specific surface area of NPCN-KOH is 1845 m2 g−1, which is much larger than that of NPCN. These unique features ensure NPCN-KOH exhibit high reversible capacity, large rate performance and long cycling life. NPCN-KOH delivers a reversible capacity of 818 mA h g−1. In addition, the capacity of NPCN-KOH cycled at 1 C for 600 cycles is as high as 527 mA h g−1, with a capacity retention ratio of 97.6%.