Polyaluminium chloride, which is a limiting factor in water purification, is a limiting factor in water purification. Polyaluminium chloride in the sewage treatment industry has been very mature, then as a water purification industry, "leader", polyaluminum chloride for all sewage purification can achieve the best? In fact, the effect of PAC water purifier is affected by many factors. The first is the impact of water quality. For example, our daily domestic water use, because this water contains a large amount of surfactant, in the treatment of this washing wastewater, polyaluminium chloride produces a large number of positively charged cations, the pollutants adsorbed and separated water body. If the suspended solids and alkalinity of sewage are low, then the effect of treatment with polyaluminum chloride is not good, usually the situation to take other types of sewage treatment methods. Second, the dosage of polyaluminum chloride can also affect the effectiveness of water treatment. Generally, the polyaluminium chloride dosage is generally adjusted according to the water quality. Third, the effect of coagulation is different for wastewater with different PH value. Under acidic conditions, the effect of PAC is not good, but in alkaline environment, it can form a stable colloidal aluminum hydroxide precipitate, Best effect. Fourth, the temperature is also an important factor affecting the effect of polyaluminium chloride. The study shows that the lower the water temperature, the lower the cohesion results. Even increasing the amount of polyaluminum chloride can not change the effect of temperature on the coagulation effect. To deal with low temperature sewage, activated silicic acid can be used to improve the cohesion effect.