The value of pH is the main indicator of catalyzed iron pretreatment of acidic wastewater and is also the controlling factor of Fe2+ generation and coagulation effect. Therefore, the change of value of pH, Fe2+ concentration and subsequent coagulation of chemical wastewater pretreated by catalyzed iron were studied.The optimum conditions of the pretreatment are 2.75of initial pH and 1hour of reaction time. The best conditions of coagulation reaction are 120mg/L of Fe2+ concentration, 8.0-8.5of pH valure. The removal rates of COD and colority are 56.8% and 92% respectively. When the pretreated chemical wastewater and printing and dyeing wastewater after being catalyzed are mixed,the optimum coagulation value of pH is 8.0~8.5.