The acoustic radiation force allows acoustic tweezers to suspend and move tiny particles. The horizontal movement is one of the common forms in which acoustic tweezers manipulate particles. In this paper, the direct relationship between acoustic radiation force and sound pressure is derived theoretically. The results show that there is a corresponding relationship between the maximum point of sound pressure (focus point) and the minimum point of acoustic radiation force potential energy. A model for focused acoustic field in acoustic tweezers is established based on the principle of phase modulating. In the numerical simulation, taking the double-sided 16-element acoustic tweezers device for example, the method of controlling the horizontal movement of particles and its stability are analyzed. Owing to the influence of gravity, the balance in the vertical direction must be considered in the horizontal movement of particles. Horizontal movement shows different stabilities at different positions in acoustic filed. The closer to the center of the array the particle is, the more stably it moves. The step length (accuracy) also has an important influence on the moving stability. In general, the shorter the step size is, the higher the stability is. In this model, when moving step length is reduced by one-half, the stability is improved by nearly 40%. The research results have theoretical significance for designing acoustic tweezers, planning particle movement paths, and promoting the application of acoustic tweezers technology.