The invention discloses an organic master batch. The organic master batch contains 500-600 mg/kg of polyglutamic acid, has a living bacterium count of 0.2-0.9 billion/g, and comprises 0-8% of nutrient in percentage by mass and 40-60% of organic matter in percentage by mass. The invention also discloses a preparation method and application of the organic master batch. Compared with the prior art, the product disclosed by the invention is low in water content and high in particle hardness, can be singly applied or mixed with a composite fertilizer, and has favorable effects in the aspects of preventing premature senescence of crops, realizing early harvesting of the crops and improving quality of the crops. Besides, the product has the effects of moisture preservation, fertilizer preservation and soil moisture preservation. Meanwhile, the preparation method of the product is simple and easy to popularize.