The invention discloses a cooling system for a server in a server room. The cooling system comprises a filtering assembly, a fan, an air conditioning assembly and a cooling tower, wherein the filtering assembly is arranged in the server room and is near an air inlet; the fan is arranged on the downstream side of the filtering assembly to lead air filtered by the filtering assembly into an air inlet channel; the air conditioning assembly is arranged in the server room; and the cooling tower is arranged outside the server room, and a water return pipeline and a water outlet pipeline are connected between the cooling tower and the air conditioning assembly. The cooling system for the server in the server room is simple, reliable, simple in maintenance, obvious in energy saving effect and capable of substantially reducing operating costs of the server room.