Abstract: Optimal ultrasonic phase array transducer parameters were deduced by use of multi-objective optimization method. Difference of normalized main lobe width and normalized pressure in far field and the amplitude ratio of the peak side lobe and main lobe at maximum steering direction were objectives respectively. The mathematic model of ultrasonic phased array was established to optimize the key geometrical parameters. The result shows geometrical parameters obtained with the method satisfy the goal of the design optimization.