When we detect an object by ultrasonic phased array focusing and steering in Non-Destructive Testing (NDT), the ultrasonic attenuation due to material damping will merge noise in the main signal and make data processing difficult. This paper presents an intensity control method developed to ensure that the intensities of eight subwaves are same when they are focusing or steering to the damage location. The mathematics model was established between eight elements and their corresponding magnification factors. We realized the intensity control function by adding an intensity controller model, which is designed on the basis of FPGA technology, into ultrasonic actuator/sensor. Some validation tests were made by using the development platform of Altera CycloneⅡseries. It was shown that both the precision and speed of the model can meet the requirement.