For the effective performance evaluation of staring imaging system, the signal response model of staring imaging system is established according to the conversion mechanism of infrared radiometric signal in the imaging process. The transfer function of imaging system is modeled using the linear system theory and sampling theory, and the noise is characterized with the three-dimensional noise model. Based on staring imaging system modeling, the triangle pattern simulation images with different differential temperatures and different sizes are generated. Triangle pattern simulation images with different stimulus intensities are observed, and the correct discrimination probability of the triangle pattern orientation is obtained utilizing the statistical method. The psychometric function-Weibull function is used to fit the probability data, and the triangle orientation discrimination (TOD) threshold prediction curve is achieved. The experimental results indicate that the triangle orientation discrimination threshold prediction curve is reasonable.