The invention discloses a method for treating organic waste gas in a chemical plant. The organic waste gas sequentially pass through a flowmeter, a flow regulating valve, a concentration monitor, a dust removal flame-retardant device, an air inlet fan, a heat exchanger, a catalyst chamber, an exhaust fan, an alkaline tower, a humidifier, a biological active packing layer containing scrap iron, a 1# electrode, a 2# electrode, a 3# electrode, a 4# electrode, a circulating water system, a thermostat, a spraying system, a three-way valve and a biological filter. According to the method, the concentration of the organic waste gas can be regulated into a proper concentration range of the waste gas treatment system. According to the method, different waste gas treatment methods can be selected according to the concentration of the organic waste gas. In the biological treatment section of the method, acidic substances in the waste gas are removed by adopting an alkali washing method, and the condition that the biological activity is influenced in the biological filter is avoided; and in the biological treatment section of the method, the scrap iron is contained in the packing, the packing is stirred periodically by utilizing the variable electrode magnetism, the phenomena that the gas flow is influenced due to blockage and the reaction is non-uniform are avoided, a stirrer can be replaced, and the inner reaction space is saved.