In order to solve the problems of low removal efficiency and high treatment cost of suspended solids(SS) in low-temperature pit water of open-pit mine in alpine regions, the water quantity and quality of the mine water from an Inner Mongolia open-pit mine were studied, and the particle size analysis and Zeta potential were used to characterize the microstructure of suspended solids in the mine pit water. Static coagulation experiments wereconducted to study the removal effect of suspended solids. The results showed that the water quantity and temperature of pit water from the studied open-pit mine were both high in summer and low in winter. Additionally, the water temperature of pit water was below 10 ℃ for 8 months in the whole year, and was below 4℃ for 7 months. The suspended solids in mine water were more than 15000 mg/L after initial sedimentation, and most of them were in the range of 0.4~1.5 μm with negative charge. The best combination at room temperaturewas polyaluminum chloride (PAC) + anionic polyacrylamide (APAM), and the best dosages were 150 mg/L and 1 mg/L respectively. The optimal coagulation and sedimentation procedure was rapid mixture stirring (200 r/min) for 2 min, flocculation stirring (60 r/min) for 15 min,and settling for 15 min. As the low temperature reduced the purification effect of coagulants, the whole year could be divided into conventional period (June to September) and low temperature period (January to May and October to December) based on10 ℃. The dosage inthe low temperature period was 20%~33% higher than that in the conventional period. After coagulation and sedimentation treatment, the suspended solids and turbidity in the effluent were less than 50 mg/L and 10 NTU, respectively, reaching the effluent standard of emission standard of pollutants for coal industry (GB 20426—2006).