Abstract: From the comparative analysis of the depth sounding data of 2006 and previous data, it is found that the Laolonggou deep trough was getting shallower and depositional in the initial stage (from 2004 to June of 2006) after the leading-to-island road constructed for Caofeidian reclamation project blocked the shoal tidal channel. This article focuses on the Laolonggou deep trough topographic change trend in the middle stage from July of 2006 to 2008 after the leading-to-island road cut off the shoal tidal channel. According to the comparative study of three depth sounding profiles crossing the Laolonggou deep trough from July of 2006 to October of 2008, it was found that the Laolonggou deep trough tended to be deeper and erosive. The reason for the depth change in this period is that the trough was partially dredged around its entrance, and a great amount of sediments up to 3~4 hundreds of millions tons has been taken from the seafloor for the need of land reclamation.