Abstract: The motion law of matter in flare loops on solar disc is discussed by using the optical observational data of the two-ribbon flare in July 14, 1980 obtained at Yunan Observatory and X-ray data of same flare from SMM. Firstly, the comparison of positions between Ha and X-ray images is used to estimate the altitude of the flare loop. Secondly, the sight-line velocity field of the flare is theoretically calculated for matter falling in flare loops, the theoretical results agree with observational data on the whole.