The unique electrochemical properties of diamond such as a large working potential window, low background current and prolonged stability make it attractive for applications in electroanalysis. Powder microelectrodes 50μm and 100μm in diameters were prepared using nanodiamonds, which were synthesized by the explosive detonation. Electrochemistry properties of nanodiamond powder microelectrodes were investigated by electrochemistry technologies, such as cyclic coltammetry, chronoamperometry and impedance spectroscopy. The results suggested that nanodiamond powder microelectrodes were electrochemically stable in the supporting electrolytes of KCl over a potential range (–0.9 ~ +1.6 V). The level of background current magnitude was 10-8 A. The electrode reaction was quasi-reversible in KCl solution containing the ferricyanide-ferrocyanide redox couple, and electrode reaction kinetics was controlled by diffusion process. The relation between peak currents and concentrations of [Fe(CN)_6]~(-3/-4) was direct ratio. The electrode of 50μm in diameter was more sensitive than the electrode of 100μm in diameter. Irreversible oxidation reaction of NO_2~- took place on nanodiamond powder microelectrodes, and the relation between oxidation peak currents and concentrations of NO_2~- was direct ratio. All of these have shown that NO_2~- could be detected by nanodiamond powder microelectrode. The results of impedance spectroscopy in the electrolyte solutions of KCl and KCl containing K_3Fe(CN)_6/K_4Fe(CN)_6 have shown that powder microelectrodes were expressed with porous characteristics. And the obtained spectra were analyzed with an equivalent circuit model.