The invention discloses a high-silicon high-plastic beta type titanium alloy and a preparation method thereof. The high-silicon high-plastic beta type titanium alloy is prepared from, by mass, 1.5%-3.5% of Si, 0.5%-3% of Fe, 1.5%-3.5% of Nb, 0.5%-2% of Ta, 0.5%-2% of W, 0.2%-2% of Hf and the balance Ti and other unavoidable impurities. Accordingly, by adding beta type alloy elements, the ductilityof the beta type titanium alloy is improved. The invention further discloses a preparation method of the high-silicon high-plastic beta type titanium alloy. The method comprises the steps that 1, a prefabricated electrode is prepared; 2, smelting and casting are conducted to obtain beta type titanium alloy ingots; 3, cogging and forging are conducted to obtain a beta type alloy forging stock; 4,rolling is conducted to obtain a beta type titanium alloy stick; 5, solid solution and ageing are conducted to obtain the beta type titanium alloy stick. Accordingly, the defects that the high-silicontitinaium alloy cogging temperature is high, and the high-temperature forging heating is conducted multiple times are overcome, the plasticity of the alloy is improved, and the phase transformation temperature of the alloy is lowered.