Abstract: Sub-bottom profiler based on Chirp signal is widely used in the fields of engineering investigation, geological hazard assessment, gas hydrate investigation and deep sea resources exploration because of its high resolution. Due to the narrow bandwidth of the Chirp signal, the side lobe of cross-correlation result is serious. Conventional extraction envelope processing can suppress side lobe, but the resolution of the data is low. In this paper, the different theoretical models and the actual data are processed by the method of mutual correlation, extracting amplitude envelope and linear frequency extraction and their results are remarkable.