The working mechanism and basic detecting ability of the SBIRS-GEO warning satellites were studied.The working mechanism is analyzed in detail from the targets detecting principles,parameter estimation principles and the basic work flow.For the basic detecting ability of warning satellites,a calculation model of detecting range is constructed.For the characteristics of satellite borne scanning and staring detectors,considering the effects of detector scale,pixel size and diffraction limit on resolution,the calculation models of basic detecting parameters are built,including target resolution,dwell time and coverage area of IFOV,etc.Furthermore,the basic detecting abilities of the SBIRS-GEO are analyzed based on typical parameters.The results can provide some references for the detecting performance analysis and system design of warning satellites.