“大学物理”旨在向学生传递“联系”与“统一”的思想，但众多的教材在推导多普勒效应公式时却没有深入探寻“相对运动”与“频率变化”之间的联系和统一．作者从波长的定义着手，基于相对性原理，应用伽利略变换式对机械波的多普勒效应公式进行推导和应用验证；采用洛伦兹变化式对电磁波的多普勒效应公式进行推导．通过推导机械波和电磁波的多普勒效应公式，揭示了多普勒效应的频率变化实际是在不同惯性系中的测量结果．

 The aim of college physics is to convey the idea of “connection” and “unity” to students, but the relation and unity between “relative motion” and “frequency change” are not explored deeply in many textbooks when derifying the Doppler effect formula. This paper starts from the definition of wavelength, based on the principle of relativity, using Galileo transformation formula to deduce and verify the Doppler effect formula of mechanical wave. The Doppler effect formula of electromagnetic wave is derived by Lorentz change formula. By deducing the Doppler effect formulas of mechanical and electromagnetic waves, it is revealed that the frequency variation of Doppler effect is actually measured in different inertial systems.