This study investigates the structural phase and dielectric properties of poly(vinylidenefluoride-co-trifluoroethylene) (P[VDF–TrFE]) thin films grown via atmospheric pressure (AP) plasma deposition using a mixed polymer solution comprising P[VDF–TrFE] polymer nano powder and dimethylformamide (DMF) liquid solvent. The length of the glass guide tube of the AP plasma deposition system is an important parameter in producing intense cloud-like plasma from the vaporization of DMF liquid solvent containing polymer nano powder. This intense cloud-like plasma for polymer deposition is observed in a glass guide tube of length 80 mm greater than the conventional case, thus uniformly depositing the P[VDF–TrFE] thin film with a thickness of 3 μm. The P[VDF–TrFE] thin films with excellent β-phase structural properties were coated under the optimum conditions at room temperature for 1 h. However, the P[VDF–TrFE] thin film had a very high DMF solvent component. The post-heating treatment was then performed on a hotplate in air for 3 h at post-heating temperatures of 140 °C, 160 °C, and 180 °C to remove DMF solvent and obtain pure piezoelectric P[VDF–TrFE] thin films. The optimal conditions for removing the DMF solvent while maintaining the β phases were also examined. The post-heated P[VDF–TrFE] thin films at 160 °C had a smooth surface with nanoparticles and crystalline peaks of β phases, as confirmed by the Fourier transform infrared spectroscopy and XRD analysis. The dielectric constant of the post-heated P[VDF–TrFE] thin film was measured to be 30 using an impedance analyzer at 10 kHz and is expected to be applied to electronic devices such as low-frequency piezoelectric nanogenerators.