Effect of co-doping two different elements and incorporating SrBi2Nb2O9 (SBN) on structure and field-stability of dielectric properties in PMNT ceramics were investigated. Single-phase cubic Perovskite structure is more easily obtained by appropriate co- doping of La3+ and Zn2+. X-ray diffraction patterns of PMNT/SBN composite showed that there is no SBN grains in PMNT/SBN as a secondary phase. Co-doping of La3+ and Zn2+ as well as incorporation of SBN markedly increased the field-stability of dielectric constant. The mechanism of improving field-stability was tentatively discussed.