Abstract:  Regarding the superimposition of the Doppler effect, the article “Phase invariance of elastic wave and transformation of plane elastic wave” states that in the case of relativity, the Doppler effect does not have superimposition. This view is not agreed in this article, through clarifying the relationship between the frequency transformation and the Doppler effect, and introducing the definitions of effect factor and superimposition properties, then analyzes this problem by using the phase invariant principle and the four-dimensional wave vector transformation, respectively. The conclusion is that the Doppler effect in the case of relativity is still superimposed.

Key words: effect factor, superimposition properties, four-dimensional wave vector, Lorentz transformation