The correlation between the crystallization temperature and ferroelectric properties is studied by the measurements of impedance spectroscopy, activation energy, dielectric breakdown strength and dielectric constant in Na0.9K0.1NbO3 glass-ceramics, while different nucleating agents are added to optimize performance. It is found that the glass-ceramics crystallized at the temperatures of the second exothermic peak (about 900 degrees C) have higher crystal degree, lager interface numbers and larger amount of bulk charges accumulated at the interfaces. However, the higher crystal degree of ferroelectric phase results in a lower value of resistivity and E-a which represent better charge spreading behavior. The better charge spreading behavior and drastic increase in the accumulation of bulk charge also result in low breakdown strength. The results show that the glass-ceramics heated at the temperature of first exothermic peak (about 700 degrees C) with a reasonable crystal degree obtain higher energy storage density which is 1.94J/cm(3).