TODT measurement method for characterizing the performance of infrared imaging sensor was introduced briefly. According to the spectrum theory, the spatial spectrum distribution of standard triangle pattern was determined quantitatively. The matched filter concept was adopted to derive the perceived triangle pattern signal and overall noise by the human visual system through infrared imaging system, respectively. On the basis of the perceived signal-to-noise ratio, the TOD performance theoretical model was first determined, and the simulated results was given. Experimental results show that this model can give reasonable prediction of the TOD performance curve for the infrared imaging system.