Abstract: The unknown parameters between space target and ground-based telescopes infrared imaging terminal reduce the dual-band pyrometry accuracy, and the influence degree is unknown. Assuming that the target is gray body, the partial derivative of maximum likelihood estimation function about emissivity is solved. The dual-band pyrometry mathematical model based on infrared detectors to measure the electron number is established, and the Monte Carlo simulation and precision analysis of dual-band pyrometry is performed. The field calibration method of atmospheric transmittance prediction based on infrared natural star is proposed. The inversion precision of space target temperature has a close relationship with the imaging detector signal-to-noise (SNR) ratio, the earth-s thermal radiation estimation accuracy, atmospheric transmittance and emissivity difference between bands. When the SNR is above 20, emissivity difference is less than 0.03, the earth radiation prediction accuracy is better than 50%, and atmospheric transmittance prediction accuracy is better than 10%, the temperature estimation precision of dual-band pyrometry is better than 40 K.