In this work, sodium niobate (NN) particles were prepared through the hydrothermal method. NN-P(VDF-TrFE) composite films with different weight ratios of NN were prepared via the casting method. The microstructure and performance of the films were investigated systematically. The results showed that the 2 wt% NN-doped P(VDF-TrFE) film had the best mechanical properties, while the 6 wt% NN-doped P(VDF-TrFE) film exhibited the best electrical performance with an output voltage of ∼5.2 V. Furthermore, the sodium niobate ceramic prepared by the solid-state reaction method and poled at DC field, was utilized to prepare the composite film for comparison. The results indicated that the P(VDF-TrFE) was of great importance for output performance. Namely, under an electric field, NN particles interacted with the P(VDF-TrFE), especially transforming the non-polar α phase of the P(VDF-TrFE) into the polar β phase, and hence enhancing the output of the composite film.