This paper aims to point out that a wave function is a description of a quantum spatiotemporal entanglement and the transformation between time and space. In any quantum mechanical representation, the real part of the wave function represents the space wave and the imaginary part represents the time wave, and they are the space-time itself. Time wave is not limited by space and dominates the nonlocality and integrity of a quantum. Matter wave is a four-dimensional space-time wave, and the basic unit of vacuum is a four-dimensional space-time element stationary relative to the observer. The essence of quantum measurement or interaction is that a conjugate condensation equivalent to that determined by inner product operation occurs between Space-time waves. Particle property is only the localization effect of quantum global collapse when quantum position measurement or equivalent interaction is made.