Correlation method based on the historical hydrology(1960-2000) of Datong station and famous Vollenweider model based on historical dam capacity, upstream discharge and total phosphorus records(1950-2006) were used to examine the filter effect of big reservoirs on dissolved silicate(DSi) flux decrease in the Yangtze River drainage basin. The historical hydrological data of Datong station showed that the flux of DSi into East China Sea obviously decreased during 1960-2000, and the net decrease flux was 1.85×10⁶ t/a, accounting for 25.3% of annual DSi flux in 1960s, the decreasing process of DSi flux was closely related to the processes of suspend sediment flux decreasing, dissolved inorganic nitrogen(DIN) flux increasing. The statistics result of reservoirs showed that the total capacity of 162 reservoirs reached to 155.4×10⁹ m³, accounting for 16.8% of annual discharge to sea; furthermore, the 54 super-big reservoirs with capacity volume > 5×10⁹ m³ including the Three Gorges Reservior, the Danjiangkou dam could contribute 87% of the total capacity of 162 reservoirs. In addition, the resident time of runoff in reservoirs was more than 0.05 year for > 90% big reservoirs. The result of the Vollenweider model showed that "biological and sediment filter effects" could occur in big reservoirs. First, the retention of DSi in 162 big reservoirs reached to 0.85×10⁶ t/a, accounted for 45.9% of the DSi net decreasing flux of 1960-2000, and 15.7% of the annual DSi flux into sea of 1990-2000. It suggest the mechanism of "biological filter" is insufficient for explaining the DSi retention process behind reservoirs, we need to develop new mechanistic models for the retention of DSi by reservoirs. Second, the result of "sediment filter" showed that retention of sediment in 162 big reservoirs reached to 6.75×10⁸ t/a, far more than the suspend sediment flux into sea of 3.41×10⁸ t/a of 1990-2000, which implicated that other decreasing DSi flux maybe primarily due to the sediment filter effect.