The direct synthesis of light olefins from syngas via Fischer-Tropsch synthesis reaction is a promising technology for direct synthesis of olefins from syngas. The key is to improve the selectivity of light olefins through the regulation of product distribution. In this work, the hydrophobic Fe@Si catalyst was prepared by room temperature solid state method- Stöber-silylation method, and then the catalyst was combined with SAPO-34 molecular sieves with different contents to prepare Fe@Si/S-34 composite catalysts. The effects of SAPO-34 molecular sieve content on the physicochemical properties of the catalysts were investigated by X-ray diffraction, scanning electron microscopy, N₂ adsorption-desorption, NH₃ temperature programmed desorption and water contact angle measurement. The results showed that the content of SAPO-34 molecular sieve has significant influence on the surface area, pore volume, acidity and hydrophobicity of the catalysts. With the increase of SAPO-34 molecular sieve content, the specific surface area and total pore volume of the catalyst increased, the weak acid and medium-strong acid sites increased, and the hydrophobicity weakened. The catalytic performance evaluation results showed that the Fe@Si/S-34 composite catalyst decomposed C₅₊ hydrocarbons into light hydrocarbons, significantly reduced the selectivity of C₅₊ products and increased the selectivity of C₂~C₄ hydrocarbons. Appropriate SAPO-34 molecular sieve could significantly improve the selectivity of C₂~C₄ olefins. When the mass ratio of Fe@Si catalyst to SAPO-34 is 2, the C₂~C₄ olefin selectivity of Fe@Si/S-34 catalyst is the highest, the conversion of CO is 80.0%, the selectivity of CO₂ in the product is 8.9%, and the selectivity of C₂~C₄ olefins is 31.1%. In this study, the hydrophobicity of Fe@Si catalyst and the cracking activity of SAPO-34 molecular sieve for C₅₊ hydrocarbon were coupled together to inhibit the water-gas shift (WGS) reaction, reduce the CO₂ selectivity and obtain higher C₂~C₄ olefin selectivity, which provided a new strategy for the development of catalysts for Fischer-Tropsch synthesis to olefins.