Abstract: For the applications of coaxial-cable electromagnetic wave reflection technique to slope monitoring, principles of the technique and the properties of electromagnetic wave propagation in coaxial cable were described herein. Based on the results of laboratory tests, the in-situ slope monitoring method with the technique was proposed. From the in-situ monitoring results, it was found out that the location of the sliding surface can be determined accurately. Comparatively, the sensitivity of coaxial cable with small diameter was higher than that of cable with large diameter.