The operating distance is one of the most important comprehensive performance indexes. Based on the imaging principle of this AlGaN solar-blind UV focal plane array (FPA) imaging system considering the influence factors of the UV system, the distance of point target and extended target are calcnlated respectively. The influencing factors of the solar-blind UV imaging system include the feature of target, the attenuation of the atmosphere transmission, optical system and UV FPA detectors. From the transfer of radiation energy of targets， the operating range theoretical formulas are deduced combing the relationship of signal-to-noise, fault prediction and detection prediction. Finally, the system parameters are inputted into the operating formula. The operating formula can provide theoretical basis for performance assessment of the UV imaging system. The operating rang can be improved by the means of increasing effective optical aperture, optical transmissivity, integration time and adopting noise reduction methods.