An optical imaging system with extended depth of focus is provided. The optical imaging system includes an optical imaging module, an array type detector and an image restoration module. The optical imaging module has a specific longitudinal spherical aberration corresponding to the depth of focus. The array type detector is coupled to the optical imaging module to obtain a image via the specific longitudinal spherical aberration provided by the optical imaging module. The image restoration module is coupled to the array type detector, wherein the array type detector converts the obtained image to a digitalized image and the image restoration module receives the digitalized image and performs an image restoration operation to the digitalized image to form an image with extended depth of focus.