The invention discloses a power filter capacitor noise reduction device and a noise reduction method. The device is characterized by comprising a sound insulation cover structure and a sound absorption cavity structure, wherein the sound insulation cover structure is fixedly arranged at the top of a capacitor body, and an air cavity is formed between the interior of the sound insulation cover structure and the top wall of the capacitor body and used for reflecting and absorbing energy of sound waves; the sound absorption cavity structure is arranged at the bottom of the capacitor body in a sealed manner. Noise sources with strong directivity at the top and the bottom of the capacitor body can be greatly reduced, so that the operation noise of the capacitor is greatly reduced.