The invention relates to the field of edible fungi cultivation and in particular to an agaric culture substrate and a preparation method thereof. The raw materials include straws, cow dung, folium cortex eucommiae, pistacia chinensis leaf, the seed of cowherb, the root of kudzu vine, soybean hulls, banana skin, wild carrot fruit and sodium carboxymethylcellulose. The method comprises the following steps: mixing the folium cortex eucommiae with water for soaking, heating until the water is boiling, adding the seed of cowherb, the root of kudzu vine and wild carrot fruit, continuously boiling for 15 minutes, cooling, adding the banana skin, heating at a constant temperature, adding sodium carboxymethylcellulose, uniformly stirring, and performing microwave treatment to obtain a product for later use; uniformly mixing the straws, soybean hulls, pistacia chinensis leaf and cow dung, fermenting, sterilizing, uniformly mixing the product for later use, airing until the moisture content of the system is 20-25%, and bagging, thereby obtaining the culture substrate. The culture substrate disclosed by the invention is balanced in nutrition, can meet nutrients needed by growth of agaric, and has high resistance to infectious microbes under the condition that the nutrition is balanced.