The invention provides an oyster mushroom culture medium and a preparation method thereof.The culture medium is prepared from, by dry weight, 75-80% of abandoned tea stems, 10-20% of cottonseed hulls, 5-10% of wheat bran, 2-5% of lime and 1-2% of saccharose.The preparation method comprises the following steps that firstly, the abandoned tea stems, the cottonseed hulls, the wheat bran, the lime and the saccharose are weighed according to the ratio, a proper amount of water is added, the mixture is mixed and stirred evenly, and a medium is formed; secondly, the medium in the first step is packaged into a culture bag, and after 4/5 of the bag is filled with the medium, an opening is sealed; thirdly, the culture bag loaded with the medium is subjected to autoclaved sterilization for 0.5 h at the temperature of 127-135 DEG C in an autoclaved sterilization pot and is cooled to the room temperature to be used.The water content of the medium is controlled within 65-68%.The abandoned tea stems are utilized, the ingredient cost of the oyster mushroom culture medium is effectively reduced, the culture period of oyster mushroom can be shortened, and the economic benefits are increased.After the oyster mushroom is harvested, the oyster mushroom culture medium can also be used as organic fertilizer.