The drawback of current area control error（ACE） is analyzed. The computation method and physical interpretation of dynamic ACE are introduced. Whereas， the current dynamic ACE only mitigates the effect of heavy HVDC and inner-area generator power lose on frequency control. Furthermore， the improvement of dynamic ACE is proposed in terms of large capacity cross-area generating set power lose and tie line constraint. The combined application of dynamic ACE， CPS and DCS is also presented. It provides a possible approach for frequency control of an interconnected power system.