A computer system and a controlling method are provided. The computer system includes a container and a display unit. The container has an opening through which a real article enters the container. The display unit displays a frame. The controlling method of the computer system includes the following steps. A first fictitious role corresponding to the real article is obtained. A space characteristic of the real article corresponding to the container is obtained. A first displaying characteristic of the real article corresponding to the frame is obtained according to the first fictitious role and the space characteristic. A first fictitious object is displayed on the frame according to the first displaying characteristic.