A new method for temperature measurement is established based on the gray-body radiation, which can not only determine the real-time temperature of thermal source, but also conduct non-contacted temperature measurement with high precision. First, a wide-band emission spectrum of the given radiation source is measured precisely with a multi-channel CCD image spectrometer, which is served as its spectral fingerprints for establishing a gray-body radiation model; Secondly, the coefficients introduced in the gray-body radiation model are determined by fitting the measured emission spectrum; Finally, a combination of spectroscopic technique and the gray-body radiation model is employed to measure any temperature of the given radiation source. Having tested on both types of radiation sources, with and without a flame, the present work has demonstrated that the imaged spectral approach mentioned above can be utilized as a real-time, high precision and non-contacted technique for temperature measurement.