Due to the cold weather in winter, the sewage water temperature is low, so it is easy to encounter problems that usually do not appear in the process of water treatment. Polyaluminum chloride is the most widely used coagulant in water treatment. It has a relatively good effect in treating high turbidity water in spring and summer. However, when the temperature is low, it will be affected by the water temperature, and the polymerization reaction speed will be reduced. The hydrolysates show more high charge and low degree of polymerization. Therefore, it is not conducive to the adsorption and bridging between colloidal particles, resulting in the characteristics of small density, not dense and not easy to sink This phenomenon leads to the floating of alum flower. However, this problem is not difficult to solve, and the use of coagulant aids can enhance the flocculation effect. The function of coagulant aids is to improve the structure of flocs and make the alum flocs which are loose and not dense become coarse and dense. The commonly used coagulant aids are polyacrylamide, activated silicic acid, bone glue, etc. Polyacrylamide has remarkable effect in treating high turbidity water, with the advantages of reducing the dosage of coagulant and the volume of primary sedimentation tank, and at the same time, it can ensure the water quality; activated silicic acid is suitable for ferrous sulfate and aluminum salt coagulant, which can shorten the sedimentation time, and has better effect on water with low suspended solids content and low turbidity, but it needs appropriate acidification degree and activation time;The molecular weight of bone glue is between 3000-80000, and the dosage is directly proportional to the water purification effect, but the price of bone glue is relatively expensive. In terms of comparative analysis, polyacrylamide is a kind of coagulant aid which has good effect on most different water quality and is relatively economical. However, Gongyi Filter Industry Co.,Ltd suggest that the choice of coagulant aid in winter should be based on the analysis of experimental results and dosage calculation.