Abstract: Intensity measure is a key parameter affecting the accuracy of seismic risk assessment. Thus based on the incremental dynamic analysis results of 12 RC high-rise structures, both efficiency and sufficiency of spectral acceleration at different periods are calculated. Then the effects of higher modes and periods softening on them are investigated. Moreover, controlling periods across the spectrum are also studied to put forward a new intensity measure which is the geometric mean of spectra accelerations values at certain periods. The results suggest that the efficiency and sufficiency are obviously fluctuated with increasing spectrum periods, and influenced by the effects of higher modes and periods softening. The proposed intensity measure is more efficient than some existing ones, showing its fitness to RC high-rise structures.