A device for a rolling mill with an adjustable offset distance in serpentine rolling and a method thereof are provided. The device includes a frame, offset moving components, upper and lower work rolls, telescopic components, lifting components, and a monitoring component. The offset moving components are connected to a middle of the frame, and the offset moving components are connected to the lower work roll bearing seats, and the lower work roll bearing seats are connected to the lower work roll; the offset moving components are fixedly connected to the telescopic components; a top of the frame is fixedly connected to the lifting components, and the lifting components are fixedly connected to upper work roll bearing seats, and the upper work roll bearing seats are connected to the upper work roll, and the monitoring component is provided at a rolling exit of the frame.