This research focused on the effect of water temperature and pH to coagulation efficiencies in low turbidity water. And the optimum dose of coagulant was determined. Simulated the treatment processing, the organic matters and turbidity removal capacities of polyaluminum chloride (PACl) were measured in parameters of turbidity, CODMn and UV254 with different experimental conditions. The results indicated that the PACl optimum doses were 28mg/L. By increasing water temperatures in the range of 4°C～18°C, the turbidity removal efficiency was gradually enhanced, while the organic loading removal performed few correlations to temperatures. And the effective pH range was 6.0~9.0, that appeared greater influence on turbidity removal than organic loadings.