Abstract: An acoustic field patterns of the High Intensity Focused Ultrasound (HIFU) are studied in this paper, and controlling algorithms of the 2-D HIFU phased array are provided. It is easy to produce certain nonlinear phenomena when a 2-D phased array uses the single-focus scanning pattern to treat large tumors. However, a directly synthesis method of the acoustic field based on the pseudo-inverse matrix can produce the multiple-focus field pattern. It provides a method for controlling acoustic field patterns. The fast algorithm of the acoustic field was used to simulate the single-focus scanning pattern and the multiple-focus field pattern produced by a phased array consisting of 30×30 elements, and simulation results show that the 2-D array using the multiple-focus pattern can produce the foci with lower intensities. Furthermore, the multiple-focus pattern also allows the complex excitation vector to be weighted to increase the array excitation efficiency, and the improved eigenvector algorithm is used to optimize the intensity gain of the multiple-focus field patterns. It is shown to increase the power deposition in the target volume and eliminate the undesired interference. And this study provides a theoretic guide to the control of ultrasonic field patterns.