An electronic system, an electronic device and a method for setting an extending screen thereof, and a projector apparatus are provided. The method for setting the extending screen includes following steps. Whether at least one projector apparatus is connected to an electronic device is determined. Moreover, when the projector apparatus is connected to the electronic device, the projector apparatus is set as at least one extending screen extended out from the edge of the screen of the electronic device. The corresponding relationship between the extending screen and the screen is related to the location relationship between the connected projector apparatus and the screen of the electronic device.