The invention provides a wave resisting device and a tank thereof. The wave resisting device structurally comprises a peripheral strip and a wave resisting plate which is in the shape of waves; the two sides of wave peaks of the wave-shaped wave resisting plate are provided with a plurality of buffering holes; the wave resisting plate comprises a front wave resisting plate body and a rear wave resisting plate body which are arranged side by side; the peripheral strip wraps and fixes the edges of the wave resisting plate so that a buffering cavity can be formed between the front wave resisting plate body and the rear wave resisting plate body. When liquid surges in a tank body pass through the wave resisting device, the surges can be counteracted between the wave peaks of the wave resisting plate and can also flow through the buffering holes to enter the buffering cavity to be counteracted, and the wave resisting effect is more remarkable; in the aspect of stress, the front wave resisting plate body and the rear wave resisting plate body of the wave resisting device each only has one side face, deviating from the buffering cavity, which can bear the flushing force of the surges, and the service life of the wave resisting device is greatly prolonged; and the buffering cavity is filled with liquid, and the strength of the wave resisting device is improved. The space, occupied in the tank, of the wave resisting device is little, and the containing capacity of the tank is not affected.