The invention relates to a yield increasing method of Alternaria tenuissima activator protein. According to the method, spores are prepared, a spore suspension liquid is prepared, and beta-sitosterol and betaine are added to a fermentation culture medium when a strain liquid is cultured, so that the yield of Alternaria tenuissima activator protein is increased. With the adoption of the yield increasing method, the culture medium and the culture conditions are optimized, so that the activator protein is increased by four times or more; ingredients of the culture medium all come from plants, the sources are convenient and safe, the cost is low, and large-scale production is facilitated; dynamic parameters of fermentation in a shaking flask are researched, and a fermentation culture medium suitable for strains to grow is acquired; influences of the inoculation amount, the initial pH value of the fermentation culture medium, the quantity of liquids in the shaking flask, the temperature and the like on fermentation are researched, and the composition of Alternaria tenuissima activator protein culture medium and the optimum fermentation culture conditions in the shaking flask are determined.