A unified form of Doppler effect was given in a reference，but it involves a third-party reference system，i. e. ，the media observation system when the velocity of wave is lower than the speed of light，so，it is not convenient to use. In this paper，a simple and unified form of Doppler effect is discussed and the proof is given.This kind of simple and unified form is given at the situation of the speed of light and far less than the speed of light. This concise form does not involve the media observation system，but also has the beauty of symmetry. And through the analysis of the formula，we get that the relativistic effect appears gradually with the increase of velocity，and is not a simple superposition of the classical Doppler effect.