The modified Bridgman directional solidification technique was used to prepare the Ni-Si eutectic composites at solidification rate of 25 μm/s. However, the formation of metastable phase Ni₃₁Si₁₂ was inevitably during solidification process. Annealing treatment was conducted to reduce the number of metastable phases. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques were used to analyze the corrosion resistance of Ni-Si eutectic composites in the 7wt% H₂SO₄ solution at 25 °C. The equivalent circuit was analyzed. Results show that the passivation performance and corrosion resistance behavior of Ni-Si eutectic composites are improved after annealing at 1050 °C for 4 h, which is mainly attributed to improvement of content and distribution of metastable phase Ni₃₁Si₁₂. The less the content of metastable phase, the stronger the corrosion resistance.