The invention discloses a low-anisotropic-index high-intensity Cu-Ni-Si alloy and a preparing process thereof. The low-anisotropic-index high-intensity Cu-Ni-Si alloy and the preparing process are suitable for cold rolling copper-based thin panels for lead frames. The alloy comprises, by chemical mass percent, 2%-3% of Ni, 0.5%-1.0% of Si, 0.1%-0.5% of Sn, 0.05%-0.1% of Fe, 0.1%-0.3% of Mg, 0.05%-0.08% of Zn, 0.2%-0.5% of RE and the balance Cu. Yttrium-based heavy rare earth is added for purifying a copper solution, and Ni2Si precipitation is improved; meanwhile, harmful texture is effectively restrained through the process that low temperature annealing is combined with grading solid dissolving before solid dissolving; and by controlling the cold rolling reduction rate, a transverse shearing belt is obtained for a product, and anisotropism is greatly improved. The alloy has the beneficial effects that the strength of extension ranges from 650 MPa to 750 MPa, the elongation ranges from 13% to 18%, the in-plane anisotropy (IPA) of the intensity is smaller than 6%, the in-plane anisotropy (IPA) of the elongation is smaller than 8%, and defects of warping, deformation and cracking of the Cu-Ni-Si alloy in the blanking process can be effectively reduced.