Abstract: In order to develop the direction property of a multi-element linear ultrasonic transducer array, the effect of its dominant frequency, element number and space between the elements on its direction was studied based on the multi-element phase-controlled technique. These results show that for good direction property, a large size array could be used when the main frequency of the transducer is low; on the contrary, for high frequency transducers, a smaller size array should be used. This is beneficial for photoacoustic detection and imaging.