A left atrial appendage (LAA) occluder and an occluding system are provided. The LAA occluder includes a sealing portion and an ablation portion arranged in the sealing portion, as well as a hollow proximal connector at a proximal end of the sealing portion. The ablation portion is connected to the proximal connector. The ablation portion is used to freeze an LAA after being injected with cryogen so as to form an annular isolation band on an inner wall of the LAA for blocking the conduction of electrical signals between the LAA and a left atrium.