Pb(Zr0.52,Ti0.48)Nb0.04O3 (Nb-doped PZT, PZTN) films are deposited on Pt/TiOx/SiO2/Si substrates with BaPbO3(BPO) buffer layers by RF-magnetron sputtering method. The magnitudes of tensile stress in PZTN films can be changed by adjusting the thickness of BPO layer. For PZTN films with 68 nm and 135 nm-BPOs, the tensile stresses measured by 2θ-sin2ψ method are 0.786 and 0.92 GPa respectively. Enhanced ferroelectric is observed in PZTN film with raised tensile stress. The remanent polarization and the coercive field for PZTN films with tensile stresses of 0.786 GPa and 0.92 GPa are 41.2μC/cm2(70.7 kV/cm) and 44.1μC/cm2(58.1 kV/cm) respectively. The leakage current decreases from 6.57×10-7A/cm-2 to 5.54×10-8A/cm-2 while tensile stress of PZTN film is raised from 0.786 to 0.92GPa. Fine XRD scan is performed with grazing incidence geometry to investigate the phase composition of PZTN films. Rietveld analysis shows that an increased tensile stress in PZTN film can promote the amount of monoclinic phase,which may be the reason for the ferroelectric property improvement.