Using two-channel detection,influences on laser radar cross section measure accuracy caused by atmosphere condition changing were studied.The new formula of comparing measure was deduced.An experiment was carried out on the new formula,and its using qualification was discussed.Through measuring the diffuse reflection board′s LRCS in the outfield,the result indicates that the new formula can correct the measure error because of the atmosphere condition changing and help to improve measure accuracy,and its calculation is very brief and carried out easily.