Food security is threatened by cadmium (Cd) contamination of rice fields. In-situ immobilization of Cd by silicon (Si) fertilizers is one of the crucial approaches to solving Cd contamination in rice fields. Various mineral Si fertilizers versus liquid Si fertilizers were compared in this study with in-situ field experiments to explore their effects and the regulating mechanisms on reducing Cd bioavailability in paddy fields as well as Cd absorption and transport in rice. The results showed that both the sprinkled mineral Si fertilizer and the foliar spray of liquid Si fertilizer significantly reduced the Cd concentration in brown rice, which was linked to reduced Cd availability in soils. Further analysis of the interaction between Si and Cd indicated that the reduced soil Cd availability and Cd accumulation in brown rice was mainly ascribed to an increase in soil pH and the available Si/Cd ratio. Among these Si fertilizers, LS and GS dominated by amorphous Si were more effective in controlling the accumulation of Cd in brown rice and declining the toxic risk of Cd on human health in rice consumption. In conclusion, Si fertilizer reduced Cd concentration in brown rice via increasing rhizosphere soil pH and available Si/Cd ratio.