The present invention belongs to the technical field of energy conversion devices, which provides an rGO-PEI/PVDF pyroelectric thin film, and the method for preparing the film, as well as a self-energized bracelet produced based on such film, which utilizes the reduced graphite oxide after modified by polyethyleneimine (PEI) (rGO-PEI) as photothermal conversion material, and the silver-plated polarized polyvinylidene fluoride (PVDF) film as pyroelectric conversion material. The rGO-PEI photothermal material is fixed to the surface of the PVDF through a transparent film, and prepare the self-energized bracelet based on it. The obtained bracelet has an output power of up to 21.3 mW/m2, and does not require additional mechanical devices to control the temperature during operation, wherein, the thermoelectric conversion, rectification, storage and application are realized through temperature fluctuation produced by absorbing sunlight during doing outdoor sports, utilizing temperature difference of air flow, and sweeping gesture, etc.