Abstract: The uncertainty principle of signal is proved according to the uncertainty principle of quantum mechanics, and is further interpreted by quantum mechanics. The signal can be considered as a kind of the quasi quantum system with wave-particle dualism. Because of the wave-particle dualism of the signal, time and frequency can not be measured at the same time. The frequency operator (FO) of signal is defined in this study, and it can be widely used in signal theory and, especially in wavelet research. The quantum interpretation for the signal explains the essence of the signal and provides the theory support for applying the framework of quantum mechanics to the signal processing.