Based on analysis of the influence factors on detecting ability of electrooptical system, a theory model of detecting ability on the influence factors is established, concept of sensitive factors of the detecting ability is put forward, an analysis method on weights sensitivity is given, and ration sensitivity research of the factors on the detecting ability is realized. Using the ration analysis method, the sensitivity of the electrooptical system is simulated under different initial conditions, and the sensitivity weights of the factors are gained. Results show that the diameter, focus, atmosphere transmittance, detecting SNR threshold, detecting pixel size and the imaging pixel numbers may influence detecting ability obviously, and detecting SNR threshold, detecting pixel size and the imaging pixel numbers change reversely with detecting ability; the sky background brightness, optical transmittance, quantum efficiency and integral time influence the detecting ability secondly, and mainly the sky background brightness change reversely with detecting ability; the ratio of obstruction influences the detecting ability least, changes reversely with detecting ability too; and the weights do not change on different initial conditions. The simulation results prove the completeness and generality of the sensitivity analysis method that can provide technical support for the electrooptical system design.