The invention provides a zirconium based amorphous alloy and a preparation method thereof. The components of the zirconium based amorphous alloy satisfies the following chemical formula (I): ZraCubAlcMdEre (I), wherein M represents one or more of Ni, Fe, Co, Mn, Cr, Ti, Hf, Ta and Nb, a, b, c, d and e are atomic percentage, a is greater than or equal to 40 and is smaller than or equal to 70, b is greater than or equal to 15 and is smaller than or equal to 35, c is greater than or equal to 5 and is smaller than or equal to 15, d is greater than or equal to 5 and is smaller than or equal to 15, e is greater than 0 and is smaller than or equal to 2.5, and the sum of a, b, c, d and e is 100. The preparation method of the zirconium based amorphous alloy comprises the steps of: a) weighing metals containing Zr, Al, Cu, M and Er respectively according to the composition of the chemical formula (I), and mixing the metals to obtain a mixture; b) placing the mixture in a smelting furnace to undergo smelting in a vacuum or inert atmosphere for 5-60min, thus obtaining a melt, with the smelting temperature being higher than the melting point of the zirconium based amorphous alloy by 50-400DEG C; and c) casting the melt to obtain the zirconium based amorphous alloy. The preparation method of the zirconium based amorphous alloy provided by the invention can be used for preparing large critical size amorphous alloys from industrial grade raw materials.