Twenty-eight water samples were collected along the main channel and four major tributaries of the Yellow River during July 2005, and which silicon isotope compositions and chemical compositions of dissolved silicon and suspended matter in water were systematically researched. The concentration of suspended matter of the different sites in the Yellow River differ obviously from 8.8 to 302120 mg/L, and which correlate with human activities (dams, pasture and farmland) and natural environment (regional rocks and vegetations) closely. The silica contents of suspended matter between 41.39 and 67.85%, very close to Loess in China. The δ30Si values of suspended matter in the Yellow River vary from -0.5 to 0.0‰, reflecting the mixture values of clay minerals (-1.9~0.0‰) and clastic minerals (-0.3~0.3‰) with different proportion. The concentrations of dissolved silicon vary from 0.68~6.90mg/L from the upper reaches to the lower reaches and their δ30Si values vary from -0.2 to 2.1‰, tends to increase from the upper reaches to the lower reaches, whilst fluctuate obviously. The trend is main correlation with the contents of carbonates and clay minerals in rocks and soils, in addition, likely to involve in the concentrations of CO2 in atmosphere and its dissolution in water. In this study, the δ30Si value of dissolved silicon output from the Yellow River to the Bohai Sea is 1.1‰, lower than the δ30Si of dissolved silicon (3.0‰)output from the Yangtze River to the East Sea, which not only provides new data for ocean silicon isotope compositions of the world rivers, and also indicates that more further and detailed investigations to other rivers with different geographic and hydrological background are very important to study global silicon cycle.