Abstract: This paper addopts conventional solid sintering method to fabricate（Ba_1-xSr_x）（Zn_1/3Nb_2/3）O₃ microwave dielectric ceramics.The influence of microstructure of systems on their dielectric properties was studied.With the increase of Sr²⁺ content,dielectric constant and temperature coefficient of system present unusual nonlinear phenomenon because of phase transition caused by tilting of oxygen octahedron which affects polarization and polarization mode.Phase transition and tilting of oxygen octahedron have no obvious effect on dielectric loss,which is influenced greatly by Sr²⁺ content and sintering temperature.