This study presents a novel elastic floating energy harvesting device with knitted PVDF thin films to convert ocean or river ripple power in harbor into useful electricity. The elastic floating energy harvesting module consists of a beating element and energy generating device. The beating element is designed by using the vertical displacement of ocean/river ripple to beat the energy generating device. The energy generating device is composed of knitted PVDF thin films with a tumbler knocking part. Because the frequency of actual ocean or river ripple is below 1Hz, the energy generating device uses the amplification factor structure to increase the beating frequency. According to different ripple situations, the knitted PVDF thin films with the tumbler shape knocking part can let the energy harvesting module transform energy more efficiently. Experiment showed that the energy harvesting module using knitted PVDF thin films can reach 0.67mW at 2cm amplitude and 0.2Hz regular ripple. Finally, the energy harvesting module can be installed on the instruments in harbor to capture the energy of ocean/river ripples.