The new piezoelectric ceramic of PbTiO3-PbZrO3-Pb(Mg1/3Nb2/3)O3 -Pb(Zn1/3Nb2/3)O3 with composition close to the morphotropic phase boundary was studied. The dielectric and piezoelectric properties of Pb0.96Sr0.04[(Zr1-yTiy)0.74(Mg1/3Nb2/3)0.20(Zn1/3Nb2/3)0.06]O3 were investigated, the composition range examined are 0.47 £ y £ 0.57. From the results of XRD and piezoelectric measurement, it is supposed that the composition with y = 0.51 corresponds to M.P.B. between tetragonal and pseudocubic perovskite. Some developed phenomena or models are introduced and take it to interpret well. After optimal choice of these conditions, the planar coupling factor close to 0.65, mechanical quality factor Qm close to 75, the longitude wave velocity close to 4100 m/s and the poled dielectric constant close to 2600 can be approached in this study.