Compared with air-based,land-based or sea-based reconnaissance,space-based infrared imaging system has more incomparable advantages,and it has been the important reconnaissance means that many military powers of the world pay attention to.Firstly,from the space-based infrared detection conditions of sea surface targets,the expression of threshold signal-to-noise ratio and equivalent band numbers were derived.Secondly,based on the first step,the expression of space-based infrared detection probability was obtained.At last,the influence of noise equivalent temperature difference,instantaneous field of view of detector,orbit altitude,zero visual range temperature difference between target and background,critical size of target and atmospheric transmittance on the space-based infrared detection probability were analyzed.The research results show that the detection probability of space-based infrared detection is relatively high for the sea surface targets with large temperature difference and size,but it is difficult to detect targets with small temperature difference and size when the atmospheric transmittance is low.The research results provide references for the design and development of space-based infrared detector.