Abstract: Trace metals and toxic metals are brought into offshore sediments and aquatic systems through various point and none-point pollutant sources, and eventually join in biogeochemical cycles. This paper made a review on the processes affecting the mobility and bioavailability of trace and toxic metals based on the research practice and current achievements made by the authors in this field. A model revealing trace and toxic metal behaviors in the offshore sediments and related aquatic system was proposed in this paper. It is suggested that the deposition of trace metals and toxic metals in offshore aquatic environment depends upon the organisms, oxidation-reduction, dissolution and precipitation, and chemical interaction in sea water, or the bioaccumulation by marine organisms. With respect to the bioavailability of these metals once they moved into marine sediments, it depends upon their relationship with pyrite and acid volatile sufide (AVS) and the mechanisms of their coprecipitation with pyrite.