Based on the clear define of lightning dectection efficiency and false alarm rate,and quantitative models is built to illuminate the influence of signal-to-noise ratio on LDE and FAR. Simulating calculation results show that to control FAR below 10%,the signal-to-noise ratio should be as big as 5.0 at least;and to keep LDE 90%,the signal-to-noise ratio should be between 5.2 to 5.7.