The composition of phosphorites from 25 Sinian, Cambrian and Devonian ore deposits in Eastern China were studied in this paper. We came to the conclusion that carbonate-f luorapatite is the main phosphatic mineral in the phosphorite of China. Hydroxyapatite can only be seen in recrystallised phosphorites occasionally. Principal associated minerals of the ore deposits are illite, dolomite and quartz (chalcedonite). According to the mineral associated relation, The phosphorites in China could be divided into five associated types. There are three important features in chemical composition of the phosphorites: First, the P2O5 contents change with types of ore, the sequence is the biogenic (35.04%), the micritic (34.88%-31.92%) the recrystallised (33.38%), the nodular (30.92%), the granular (29.01-28.14%) and the sandy (21.37%). Secondly, the P2O5 contents of ore change with mineralization areas, for example, the average P2O5 contents of the Cambrian ore in North China Platform and Yangtze Platform are 21.3% and 30.18% respectively. Thirdly, they change with mineralization epochs. With the squence of Sinian, Cambrian and Devonian, the CO2/P2O5 ratios reduce from 0.15 to 0.04; MgO, CO2, MnO and K2O-contents are from higher to lower; however, the Al2O3 is in a converse case. Generally, the compositional differences of phosphorites in China are determined by the differences of mineralizational background, environments, facies characteristics and mineral paragenic types primarily.