Abstract: Aiming to solve the problems that the ultrasonic signal is characteristic of high attenuation,high scattering and high structural noise, and the flaw signal is hard to obtain and hard to be identified when detecting concrete with ultrasonic testing,this paper presents a synthesis aperture focusing technique(SAFT) to process signal aiming at enhancing the resolution ratio and SNR of the imaging. Firstly,a numerical analysis software WAVE 3000 is employed to build a three-dimensional concrete model which is used for simulating the ultrasonic propagation process inside the concrete. The experimental research is then developed on the system which is set on a large size concrete block samples. The imaging results show that the algorithm can enhance the power of ultrasonic echo signal around the defects and weaken the power of noise signal,which improves the signal SNR of the defect and shows the actual position of the defects,providing reference for concrete testing with ultrasonic.