The invention discloses a flexible piezoelectric composite film and a preparation method thereof, and belongs to the technical field of composite material preparation. In the invention, nano-SiO2 particles are added to PVDF, crystalline phase transformation is promoted by adopting a high-rate uniaxial tensioning method, the content of beta phase in the PVDF material is increased, then two sides ofa film are coated with conductive silver paste electrodes, and the material is polarized at a high voltage and thus the material hs excellent piezoelectric property. The preparation method disclosedby the invention has high operability and is easy to control, and the prepared composite film product has good quality.