Abstract: Regarding wave speed and wavelength transformation, although it has been discussed in some literatures, but the obtained expressions is too complex to be remembered, and its physical significance is not involved. This article analyzes this problem by the Lorentz transformation of four-dimensional wave vector, through introducing the concept of wave speed factor and comprehensive velocity factor, the simple expressions that are easy to remember is obtained, and strive to clarify its physical significance, and finally explain its application.

Key words: four-dimensional wave vector, wave speed factor, comprehensive velocity factor