1. A temperature-detecting system arranged in a data center to monitor the temperature of the data center, the temperature-detecting system comprising: a plurality of detected-objects arranged in a plurality of cabinets in the data center; an infrared image-detecting apparatus arranged corresponding to the detected-objects; and an image-processing apparatus electrically connected to the infrared image-detecting apparatus, wherein the infrared image-detecting apparatus derives a lens-frame image; wherein the locations of the detected-objects required temperature detection in the lens-frame image are obtained by the image-processing apparatus; wherein the color of the locations of the detected-objects required temperature detection in the lens-frame image are analyzed by the image-processing apparatus to derive related temperature data; wherein the data corresponding to the shape of an edge of the detected-object is memorized in the image-processing apparatus, so that the lens-frame image is compared by the image-processing apparatus to decide the locations of the detected-objects required temperature detection.