A pair of viewing glasses and an image beam adjustment method are provided, wherein the viewing glasses includes a polarizer. The adjustment method includes the following steps. Detect the transmittance of the image beam from the screen passing through the glasses. Generate an operating signal according to the operating period of the viewing glasses, a corresponding value corresponding to the operating period of the viewing glasses, and the transmittance of the image beam, so as to adjust the polarization direction of the image beam before passing through the polarizer. Maintain the operating signal during the operating period of the viewing glasses.