Abstract: Rainfall is an important factor to induce the instability and deformation of pit slope,mainly through the re- duction of potential sliding surface ( band) rock mass intensity to induce landslides. A large number of studies have been carried out on the mechanism and stability evaluation of bedding landslide along the footwall of Nanfen open-pit iron mine stope,and a lot of achievements have been obtained. However,all the research results show that the potential sliding surface (rock) of the slope is weak in water absorption,and the mechanism of the slope stability affected by water is not clear. In this paper,firstly,the experiment of water absorption and softening of chlorite amphibolite on the potential sliding surface (band) is carried out by using a self-developed “intelligent testing system for vapor water ab- sorption of soft rock”,to reveal the characteristics of water absorption and the change of strength attenuation after ab- sorbing water;then,using Image-pro Plus professional image processing technology,the SEM image is analyzed;final- ly,the relationship between the micro-pore structure characteristics and the characteristics of water absorption is re- vealed. The results show that ① The water absorption of chlorite amphibolite increases rapidly in a short time and then decreases to uniform saturation;② The main factors affecting the water absorption characteristics of chlorite amphibo- lite are the pore structure characteristics rather than the content of clay minerals;③ There is a positive correlation be- tween the pore accumulative volume (total pore volume) and water absorption characteristics;④ The smaller the pore diameter of the concentration distribution,the greater the proportion occupied,the worse the water absorption capacity of the rock is;⑤ The water absorption rate of chlorite amphibolite is negatively correlated with uniaxial compression strength and elastic modulus. The above results provide a theoretical basis for the prevention and control of landslide induced by rainfall in Nanfen Open-pit mine.