Sinoma Xiangtan Cement Co., Ltd. has a 5 000tpd cement production line with 2 sets of roller press cement combined-grinding system. One of the system was designed as open-circuit ball mill. After putting into operation，this open-circuit grinding system appeared many problems such as high products temperature，low capacity，more power consumption etc. In 2018，in order to improve products quality and reduce power consumption，the company implemented modification and optimization on this system，mainly，modificated it to a closed-circuit ball mill system with a high efficiency dynamic separator. After commissioning period，the capacity achieved 200t/h and SPC is 33kWh/t for P·C32.5 type cement. When produce P·O42.5 type cement, the capacity is about 205t/h ＠360±15m2/kg blain, and NC 26%～27%. Moreover, this system can be production in open-circuit or closed-circuit mode alternatively according to the requirements.