Modal aliasing problem exists in empirical mode decomposition for the decomposition of transient power quality disturbances, and high-frequency harmonic injection based EMD (HF-EMD) is a simple and efficient method to improve it. The effectiveness of this method depends on the selection of the frequency of the high-frequency harmonic, and there is no effective frequency selection principle. Focusing on this problem, this paper conducts a systematic study, and through theoretical analysis and simulation test, a concrete and effective selection principle is presented. That is to say, when the injected frequencies are in the range from the smallest frequency of the original signal’s high-frequency components to adding a 1/2 times fundamental frequency of the smallest frequency, HF-EMD shows general validity. The analysis of power quality signals simulated by PSCAD and the actual complex disturbance signals of substation shows that this principle is efficient and universal. The detection accuracy of transient power quality disturbances can be effectively improved.