Practice has proved that in using traditional pre-stressed cable for the monitoring and early warning of open-pit mine landslide, cables would fracture and result in failure of the whole monitoring system when sliding force is higher than the material strength of pre-stressed cables. In view of this, Prof. Manchao He developed a system of anchor cables with high constant resistance for monitoring large deformation. The system has been used in open-pit mine for landslide monitoring. In this paper, the effect of negative Poisson’s ratio of the cables is revealed in geometric and strain dimensions through indoor static tensile tests. The structure of the high constant-resistance cable is described, and the working mechanism of monitoring large deformation is analyzed by establishing a mechanics model of high constant resistance. Results manifest that the cable of high constant-resistance can be stretched to a maximum of 850 mm with a constant resistance of 500 kN. The cable has been applied to the safety monitoring of slope at Nanfen open-pit iron mine, and provided monitoring and early-warning for the landslide on 31^st July, 2010.