In this paper, the typical hazards - seawater intrusion have been chosen to investigate the coastal geological hazard assessment method. The fuzzy hierarchy comprehensive evaluation approach based on GIS is presented to study and demonstrate the main principle and process of coastal hazard assessment. Among these, the hierarchy analysis method is used to define weights of each assessment factors, and the fuzzy comprehensive evaluation method is used to determine membership value. The realization of hazard assessment is carried out through space grid overlay analysis by GIS tool. Then, taking Bao'an district of Shenzhen as example, we carried on hazard assessment on seawater intrusion by using fuzzy hierarchy evaluation method based on GIS.