In order to obtain excellent electrical properties and its temperature stability of KNN-based ceramics to meet the practical applications, a new lead-free material system of (1-x)K0.5Na0.5Nb0.96Sb0.04O3-xBi(0.5)Na(0.5)Zr(0.8)Sn(0.2)O(3) (KNNS-xBNZS, 0 <= x <= 0.060) was designed, and the enhanced electrical properties (eg, d(33) similar to 465 pC/N, epsilon(r) similar to 3318, S-uni similar to 0.133%) is obtained in the ceramics with x = 0.04. The physical origin of enhanced electric properties should be ascribed to the phase instability of R-T, resulting in a low-energy barrier, which can greatly facilitate the polarization switching. Moreover, the temperature stable of piezoelectric constant (d(33) or d(33)*) is measured by three distinctive methods in different phase boundaries (O, O-T, R-T) at the temperature range 20 degrees C-180 degrees C, revealing that the O-T phase boundary has a relatively good temperature stability. A mode is used to show how to effectively modified the piezoelectric constant (d(33) or d(33)*) and its temperature stability, we believe that such a strategy may further improve the temperature stability of d(33) or d(33)* value in KNN-based ceramics.