This application discloses a head mounted display device for extending a display area of an electronic device and a processing method of the head mounted display device. A display of the electronic device displays first content of an image. The image further includes second content that is not displayed on the display of the electronic device. The head mounted display device obtains, by using an image sensor, the first content displayed on the display of the electronic device, performs projection transformation on the second content, and displays the obtained first content and the second content obtained after the projection transformation on the display of the head mounted display device.