There exists a special phenomenon of control performance standard（CPS） indicators related to load scales of control areas in China Southern Power Grid: the distribution of CPS1 indicators in control areas with great disparity in load scales is markedly different from one another. By an in-depth analysis of the principles of the North American CPS and an investigation on and confirmation of the generation mechanism of this phenomenon， it is pointed out that， because of the overall nonlinear positive correlation between the average fluctuation of area control error（ACE） and the frequency response factor， there is the problem whether CPS is applicable to control performance assessment for areas with great disparity in load scales. An adaptability adjustment method for using the North American Electric Reliability Corporation（NERC） CPS is proposed by introducing the average amplitude of medium-short cycle load fluctuation of the controlled area. Simulation results show that this method is capable of eliminating the peculiar phenomenon of distribution of CPS1 indicators in areas with great disparity in load scales， solving the applicability problem.