Abstract: High density polyethylene pipes are widely used in the field of gas delivery, and the welding quality of the butt fusion joint directly affects the safety of the pipe system. Imaging experiments of the side-drilled hole defects of high density polyethylene test blocks are performed by using the total focusing method. The imaging effect and quality are improved by signal preprocessing, and a total focus imaging method of ultrasonic array based on half sparse matrix capture is proposed and compared with total focus imaging results obtained by total matrix, half matrix and sparse matrix capture. The result show that the total focus imaging method based on half sparse matrix capture can effectively reduce the amount of calculated data and improve the on-site real-time detection efficiency. It can also be used for the reconstruction of side-drilled hole defects in high-density polyethylene materials without significantly reducing the signal to noise ratio of image.