Abstract: According to generating mechanism of Gravity Earth Tide, this paper introduces a new approach of three-dimensional orthogonal decomposition model to decompose the signal because the traditional method of Gravity Earth Tide fails to classify the harmonic into series.In this three-dimensional orthogonal decomposition model, Gravity Earth Tide is divided into three parts which is orthogonal of each other.In order to get the geophysical information according to the decomposed model, this paper introduces the method of Independent Component Analysis (ICA) to separate the Gravity Earth Tide.At the same time, in order to get the best solution matrix, this paper uses the mutual entropy as the optimization function and the Particle Swarm Optimization algorithm (PSO) as the optimization function.Through experiments, the results are consistent with the three-dimensional orthogonal decomposition model, and frequencies are consistent with theory values.