The temperature during the brain tumor therapy using high-intensity focused ultrasound (HIFU) should be controlled strictly. This research aimed at realizing uniform temperature distribution in the focal region by adjusting driving signals of phased array transducer. The three-dimensional simulation model imitating craniotomy HIFU brain tumor treatment was established based on an 82-element transducer and the computed tomography (CT) data of a volunteer's head was used to calculate and modulate the temperature distributions using the finite difference in time domain (FDTD) method. Two signals which focus at two preset targets with a certain distance were superimposed to emit each transducer element. Then the temperature distribution was modulated by changing the triggering time delay and amplitudes of the two signals. The results showed that when the distance between the two targets was within a certain range, a focal region with uniform temperature distribution could be created. And also the volume of focal region formed by one irradiation could be adjusted. The simulation results would provide theoretical method and reference for HIFU applying in clinical brain tumor treatment safely and effectively.