Based upon the comparisons between underwater bathymetries digitized from nautical charts (1936~2002) and between coastlines derived from two landsat-5 TM images (1986~2007), the hazardous geology associated with erosion and deposition was analyzed for the past 70 years. During the last century, the sedimentary pattern was divided into nine types according to the depositional rates. The results show that the slight sedimentation happened as a whole in Jiaozhou Bay from 1936 to 1963. Unlike before, the deposition obviously decreased from 1963 to 1982 and then the sedimentary environment transferred into the equilibrium. Subsequently, most of coasts extended obviously towards the sea between 1986 and 2007. Moreover, the analysis of tidal prism and cross-sectional area of tidal inlets shows that the current velocity amplitude and the corresponding equ-coefficient of friction had decreased over the past 70 years in Jiaozhou Bay. This indicates that the entrance of Jiaozhou Bay tended to be relatively instable.