ccording to the similarity theory and research experience on rock and soil slopes, the change regularities of stress field, displacement field, and medium strength of slope in the size similarity transformation are discussed in the paper. It is proved that with the slope size magnification in similarity scale Cl, the quantity of stresses will be amplified linearly in the same scale, but the shape of stress trace network will keep the same; the displacement will be amplified in a scale ofC 2l, the strength of slope medium will be decreased in a function of inverse proportion with Cl , and the failure surface will be inward shift. It also indicates that while both size and medium change simultaneously, the displacement, strength, and the shape of failure surface will also change in their special regularites. An example is given to prove the theoretical results above. The results will be helpful to research of engineering behavior of high slope.