The invention relates to the technical field of image processing, and particularly relates to a method, a device and a system for trying on glasses in a virtual mode. The method provided by the embodiment of the invention comprises the steps of establishing a three-dimensional coordinate system according to an acquired face image, positioning a selected pre-established three-dimensional glasses model on a pre-established three-dimensional face model, then positioning the three-dimensional face model on a face image model in the three-dimensional coordinate system, scaling the three-dimensional face model so as to enable the three-dimensional face model to be matched with the face image model in the three-dimensional coordinate system, and displaying the three-dimensional glasses model and the face image model. Through the method, the device and the system provided by the embodiment of the invention for trying on the glasses in the virtual mode, users are enabled to show effects after wearing the glasses visually and realistically without a need of actually wearing the glasses, thereby improving the try-on efficiency of the glasses. In addition, a problem of waste which is possibly brought about by resource duplication of the glasses can also be improved, thereby reducing the cost, and reducing inventory pressure.