Abstract: The piezoelectric energy harvester which can convert mechanical energy into electrical energy provides a continuous and independent power supply scheme for portable wearable electronic devices, and promotes the development of flexible electronic technology in the direction of intelligence, integration and multi-function. In this paper, Ag nanoparticles decorated potassium sodium niobate (KNN) particles were synthesized by the method of photoreduction, which were compounded with polyvinylidene fluoride (PVDF) to obtain Ag-KNN/PVDF piezoelectric composite films. Then, the flexible composite piezoelectric films with sandwich structure (PAKP) and piezoelectric flexible energy collectors were prepared by thermal pressing Ag-KNN/PVDF film with upper and lower layers of PVDF. The results show that when the amount of Ag nanoparticle is 1% mole fraction, the piezoelectric output performance of PAKP flexible composite film is the best, the output voltage can reach 6.39 V, which is 1.43 times that of the sample without Ag decoration, and the maximum instantaneous power of the device is 150.5 nW. After 3000 cycle tests, the voltage output amplitude of the device has no obvious decline. The 220 nF capacitor can be charged to 1.2 V in 200 s by fixing it on the bicycle frame and collecting the mechanical energy of the bicycle, which shows that it has a good application prospect in the field of self-power supply of low-power electronic devices.