Sound velocity measurement is one of the basic contents of college physics experiments，and some special phenomena appearing in the process of practical operation are worth to discuss deeply. This paper studies mainly the two phase synthesis phenomena (i.e.，secondary wave phenomena) and proves its existence through concrete experimental measurement and gives a theoretical explanation according to the simulation numerical solution of Mathematica software. Based on the results，the principle of the resonant interference and phase comparison methods for measuring sound velocity is discussed. The asynchrony between the measurements is shown，and the qualitative explanation is given.