Abstract: The memory effect of RF power amplifiers is the main reason for preventing a power amplifier from achieving uhra-linearity with traditional memoryless predistortion techniques. It is possible for quantitatively comparing the strength of the memory effects of the different RF power amplifiers by accurately identifying the memory effects and calculating their magnitudes so as to linearize power amplifiers with different linearization techniques. In this paper, it is discussed how to remove the time-delay of a power amplifier in order to extract the equivalent baseband characteristic of the power amplifier excited by practical modulation signal at first. Then the identification approach of the memory effect using the memoryless predistortion techniques is discussed. The calculation method for the strength of the memory effects, which is based on the spectral analysis method, is proposed. Finally, through the experimental test and calculation for the different RF power amplifiers excited by a variety of modulation signals, it is demonstrated that the proposed method is an effective means for evaluating the strength of memory effect of an RF power amplifier.