Pipeline defect detection is a necessary means to ensure the safe operation of pipeline system, and this paper uses the method of full focus imaging to image and identify pipeline defects. The finite element software ABAQUS is used to conduct numerical simulation of the pipeline defect detection method based on L(0,1) modal guided wave, and the signal is preprocessed by median filtering, Hilbert transformation and signal envelope sharpening method, and then the processed signal is used to construct the full matrix data, and finally the defect imaging is realized by the full focusing algorithm, and the imaging results are finally displayed. Experimental results show that the signal is pre-processed and then imaged, which can effectively improve the resolution and achieve high-precision visualization of defects.