An interactive stereo display system and a method for calculating a three-dimensional (3D) coordinate are provided. The interactive stereo display system includes a plurality of interactive devices, a stereo display panel, and a processing unit. When the stereo display panel is irradiated by a light radiated from a light source of each interactive device, an image of each light filtered by a color filter is captured by an in-cell type optical sensor array. After receiving the images, the processing unit determines overlapping circle objects in each image and identifies the circle object formed by each light source according to a light intensity value at the center of each circle objects. Accordingly, the 3D coordinate of each interactive device relative to the stereo display panel can be calculated according to the center and a radius of each circle object corresponding to each light source.