Satellite-borne photoelectric imaging system can detect space objects effectively and detection distance is an important parameter to evaluate system performance. System detection distance model influenced by the number of imaging pixel is established, detector sensitivity, signal-to-noise ratio and imaging resolution respectively and derive detection distance equation based on sun radiation and deep space radiation character. And then relations between detection distance and exposure time, pixel size and optics effective aperture are simulated. The results show that the maximum detection distance is 12 km which is limited mainly by imaging resolution when object size is 2 m × 4 m , average reflectivity is 0.3, optics effective aperture is 100 mm, detector pixel size is 3.5 μm and focal length is 500 mm. The result can provide theory guidance for the design and system performance evaluation of the satellite-borne photoelectric imaging system.