The stretching is one of the most effective methods to improve the piezoelectric property of PVDF-HFP films. In this paper, PVDF-HFP piezoelectric films were prepared by solution casting method. The evolution in morphology and crystal structure of the films during stretching was studied by adjusting stretching rate and stretching temperature. The results indicate that the stress along the tensile direction can force the internal structure of the matrix to transform from spherical crystals to fibrous crystals, thereby promoting non-polar α-phase transition to polar β-phase. With the parameters that stretching elongation 5, the stretching temperature 60 ℃ and the stretching rate 10 mm/min, the relative content of β-phase in this film exceeds 90 %, the calibrated open circuit voltage reaches 1.5 V under the maximum poling electric field of E_max = 60 MV/m. Furthermore, when the maximum poling electric field increases to E_max= 100 MV/m, the calibrated open circuit voltage of the film increases to 2.24 V. The higher maximum poling electric field results in a more complete orientation of the inherent dipole moment inside the matrix and better piezoelectric performance.