A systematic and detailed comparison between two standards to characterize imaging IR system performance-minimum resolvable temperature difference/minimum resolvable contrast (MRTD/MRC) and triangle orientation discrimination threshold (TOD) is presented. Many differences between them, such as test pattern, measurement procedure, applicability and target acquisition(TA) performance prediction accuracy are described. Then the precise analysis is given for these differences. Finally, the application of TOD method in the performance evaluation and testing field of imaging IR system is prospected.