This invention relates to a Cu-Zr-based amorphous alloy, whose general formula is (Cu1-xZrx)aAlbMc, where, x is 0.40-0.60; a is 80-100; b is 0-14; c is 0-20; a + b + c is 100; M is Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Ti, Ag, Ga, Hf, Ta, Nb, Ni, Co or Fe. The preparation method comprises: (1) mixing Cu, Zr, Al and M according to the ratio in Ti-adsorbed Ar atmosphere in an arc furnace, smelting and cooling to obtain mother alloy ingot; (2) re-melting the mother alloy ingot in air, and casting into a water-cooling metal mold to obtain the Cu-Zr-based amorphous alloy. The alloy has high glass formation ability, high crystallization inhibition and large size at a very low cooling speed.