An acoustic field pattern of the High Intensity Focused Ultrasound (HIFU) is studied in this paper. There are many kinds of focusing methods. Electrical focusing is one of them. Comparing with other kinds of focusing electrical focusing has a lot of merits, but there are some contradiction conditions in its design. A direct 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 is used to simulate the multiple-focus field pattern produced by a phased array consisting of 1313 elements. The simulation results show that the 2-D array by using the multiple-focus pattern can produce the foci with lower intensities. Furthermore，the genetic algorithm is used to optimize the intensity gain of the multiple-focus field patterns. It is shown that HIFU can increase the power deposition in the target volume and eliminate the undesired interference.