Pelagic sediments are the place where polymetallic nodules grow.The present paper has systematically studied geochemical characteristics of hydrogenic components of main ore-form-ing elements within sediments in different geochemical fields and at different sedimentary stages as well as the relationship between contents of hydrogenic components and mineralizaton. Studies show that Mn,Fe,Co,Ni and Cu are some fairly active elements existent together in an unified system of polymetallic nodules,sediments and ocean water. When nodules are formed,Mn Fe,Ni and Cu contents in nodules are in negative correlation with their contents in sediments,whereas things are just the opposite for Co content.Nodules in the eastem part of the study area are characterized by rich Mn, Ni, Cu and poor Fe, Co, while sediments asso-ciated with these nodules are relatiyely deficient in Mn,Ni,Cu, Co but rich in Fe, and canthus be called an impoverished geochemical field.Nodules in the western part of the study area are rich in Fe,Co but deficient in Mn,Ni, Cu,whereas their saaociated sediments are corre-spondingly poor in Fe but rich in Mn,Ni,Cu,Co,and can hence be called an enriched geo-chemical field.It is thus known that the impoverished sediment geochemical field is just the best place in search for rich ore nodules.Corresponding to the formation of nodules,the sedi-ments since Early Miocene,in accordance with contents of content ratios of hydrogenic compo-nents,can be divided into three major sedimentary stages.of which No.Ⅱstage shows geo-chemical characteristics of impoverishment,and is the most favorable period for the formation of polymentallic nodules.