Abstract: Focusing on the problem of ultrasonic phased array in pipeline inspection, this paper analyzed the principle of propagation of ultrasonic wave radiated by ring ultrasonic phased array in the pipeline, and established the focusing mathematical model. The delay of the excitation signal between the elements was calculated. The experimental results of the 128 elements transducer on the φ168 mm pipeline show that, the delay rule of the ring ultrasonic phased array realizes the focusing of the acoustic beam in the wall under the conditions of different working elements and different focal length, and a certain number of array elements in the working array element range can achieve good focusing effect.