High Energy ball milling is a simple and effective method in preparing nano-particles, which can be used to low size of starting dielectric powder for building thin casting film, favoring to enhance the capacitance density of multilayer ceramic capacitors. In this paper, Bi_0.5Na_0.5TiO₃-NaNbO₃ (BNT-NN) binary system has been selected as research goal. After high temperature calcining, the obtained pure phase BNT-NN coarse powder has been further pulverized by high energy milling method. The results revealed that high energy milling method can realize the refinement of BNT-NN nano-powders in a short time. Using these nano-powders as precursor, the grain size of the densified ceramics decreased about one third in comparison with those derived from normal coarse powders. Moreover, the temperature stability of capacitance of fine ceramics was below 15% in a wide temperature region between -60_oC to 300_oC, showing potential application in high-temperature multilayer ceramic capacitors.