Abstract: A numerical model for studying the evolution of interactions among coherent gravity wave packets in a two-dimensional space is developed. With this model the complete evolution of interactions caused by the collision between two large-amplitude wave packets is revealed. Numerical results show that downgoing gravity waves can be excited by upgoing gravity waves through interactions. During the evolution process of these interactions, the energy budget of three wave packets and the intensity of interactions are localized. Since the spatial propagation is included, the interaction process is no longer Periodical and then a new characteristic time arises, which has completely different meaning compared with the previous one. This new characteristic time and the final developing level of interactions are determined not only by wave interaction coefficients and the initial amplitudes of wave packets, but also by wave packet spatial scales and the relative magnitude of wave group velocities.