0.7Pb(ZrxTi1−x)O3–0.1Pb(Zn1/3Nb2/3)O3–0.2Pb(Ni1/3Nb2/3)O3 (0.7PZT–0.1PZN–0.2PNN, x=0.44–0.47) piezoelectric powders and ceramics have been prepared through conventional solid-state reaction method. Outstanding piezoelectric and dielectric properties occurred at the morphotropic phase boundary (MPB), which was characterized by the X-ray diffraction spectrum. The MPB composition (x=0.46) performed high d33 value (641pC/N), indicating that the system suited large-strain application. The field-induced strain reached 0.25% under a considerably low electric field (0.8kV/mm) according to the bipolar strain *S–E loops. The effect of the grain size on the aging phenomenon and temperature stability has also been investigated. Due to higher Curie temperature and smaller grain size, the 0.7PZT–0.1PZN–0.2PNN ceramics maintained a high d33 level after depoling treatment, revealing a superior strain capacity for high-temperature application.