A display device and controlling method thereof are provided. The display device includes a connecting port, an image capture module, and a data exchange module. The image capture module is configured to generate image data, and the data exchange module has a data transmission bandwidth. The controlling method comprises following steps of: generating image data with a first resolution by the image capture module when the computer host is electrically connected to the connecting port and executes a login procedure; and generating the image data with a second resolution by the image capture module when the computer host ends the login procedure; wherein the first resolution is lower than the second resolution.