The invention discloses a device for treating jelly in lake water with an activated sludge process and a removal method thereof. The device is composed of a raw water pond, a raw water delivery device, a steady settling pond, a muddy water stirring device, a sludge discharge pipe, an aeration pond water input device, an aeration pond, a sludge pond, an aeration device, an aeration pond water output device, a settling pond, a clean water pipe, a clean water pond, a sludge backflow device, a support and a control system. Raw water enters the steady settling pond through the raw water delivery device, sludge generated after primary settling is discharged into the sludge pond through the sludge discharge pipe, sewage generated after primary settling enters the aeration pond through the aeration pond water input device, aerobic microorganisms degrade the jelly under the condition of oxygen supply of the aeration device, the jelly enters the settling pond through the aeration pond water output device after being treated, clean water generated after secondary settling is discharged into the clean water pond, and activated sludge generated after secondary settling flows back into the steady settling pond for cyclic action again. The device for treating the jelly in the lake water with the activated sludge process is high in purifying rate, capable of achieving even muddy water stirring and wide in application range.