Abstract: According to the newly issued “Emission standard of air pollutants for cement industry (GB 4915-2013)”, the emission concentration values of dust collectors for cement kiln and grinding system have been restricted to less than 20mg/Nm3 in important protection areas. However, the designed value of existed bag filter reformed from ESP is 30mg/Nm3. How to meet the increasingly stringent environmental regulations according to the second modification of existed bag filters reformed from ESP with least investment is the key issue for cement plants. Based on the filter mechanism, the optimized method to decrease the emissions is to increase the filter area and reduce the filtration velocity. The aim can be realized in practice by means of CFD simulations and adding new bag compartments.