The invention discloses a real-time image viewing method in telemedicine for super-sized medical images, such as pathological slice images. According to the real-time image viewing method disclosed bythe invention, a partial thumbnail of the image is generated in a server processing mode, a thumbnail mapping method and a caching method of different zooming levels are designed, and a cache updating method is designed to save the storage space. When a client requests image data, and the server firstly determines whether to hit the cache, and generates thumbnails of a specified window and a zoomlevel in real time if the cache is not hit. The client reduces the operation delay of the image tuning window (such as dragging, zooming) by means of preloading. By monitoring a mouse (touch) event,whether the user stays in a certain area is judged through a certain rule, if the user stays in the area, the thumbnails of the next few levels of the staying area are preloaded, and a clear image ofthe target area is viewed in real time.