A display method is applicable for a display apparatus. The display method includes transmitting preview data outputted by a client terminal to a host terminal such that the host terminal displays a preview image corresponding to the preview data. After the host terminal displays the preview image, if the host terminal outputs a first display permission signal, the display apparatus is utilized to display an image corresponding to an image signal outputted by the client terminal. A display apparatus, a video system and a projector are disclosed herein as well.