Abstract: Two signal processing approaches are presented to improve imaging resolution in ultrasonic NDT of concrete structures.When low-frequency B-scan data are processed by Synthetic Aperture Focusing Technique (SAFT), wavepacket will be further elongated because low-frequency detection signal covers a relative long period.Wavepacket Decomposition Technique (WDT) is introduced here to solve this problem.This method uses a few parameters to describe the original signal so that it can avoid the processing of the whole time history of signals.In practical measurement,ringing of commercial ultrasonic transducers also affects the discrimination of the detected signal,a method based on digital filtering is proposed to build the compensation model of transducer system.By eliminate the ringings with the filter,the spatiotemporal resolution of ultrasonic imaging is improved.Numerical simulation and experimental results have proved the efficiency of the methods.Imaging resolution is improved obviously and the embedded object in a test specimen is located accurately.