The invention relates to repair and protection technologies for agricultural soil pollution and quality degradation and in particular to a soil repair agent and a preparation method thereof. The soilrepair agent comprises the following components in parts by weight: 9-25 parts of cross-linked gamma-poly glutamic acid, 10-20 parts of probiotics liquid, 1-10 parts of pesticide detoxifying enzymes and 40-80 parts of an adsorbent. According to the soil repair agent disclosed by the invention, the pesticide detoxifying enzymes, poly-glutamic acid, probiotics and organic matters are effectively combined, and pesticide residues in the soil are decomposed by utilizing the pesticide detoxifying enzymes, so that soil environment deterioration caused by pesticide residues can be effectively contained, and beneficial microorganisms are prevented from being killed; by utilizing complexing property and biocompatibility of the poly-glutamic acid, plant root development is promoted, the root absorption capacity is enhanced, and the crop resistance is improved; physical and chemical properties and granular structures of the soil can be repaired by utilizing the organic matters, and the soil fertilizer and water retaining capacity is improved.