An array of condensations trapped in one-dimensional (1D) optical lattice is used as a source of coherent matter wave to investigate the coherence properties of the Bose-einstein condensates (BEC). The macrowave function for matter wave interference is given. Based on the wave function, the distribution of particle number density, particle current density, velocity of interference peak movement and phase of the macrowave function were studied. The evolution of the interference pattern under a varible relative phase difference between successive optical lattice sites is also discussed. The research shows that the peak of interference is a wave packet with a fixed velocity, the wavelength satisfies the relation of de Broglie, and the evolution of the wave packet phase can be approximated by the classical plane wave.