The invention discloses a preparation method of a biofertilizer, belonging to the technical field of agricultural fertilizers. The preparation method of the biofertilizer comprises the following steps: uniformly mixing plant lactobacillus, phosphate solubilizing bacteria, potassium solubilizing bacteria, a bacillus subtilis culture and an aspergillus awamori culture in proportion; putting the mixture into a granulator to be granulated, controlling the grain sizes between 0.5mm and 2mm, then enabling the fertilizer granules to adhere to added humid polyglutamic acid, then controlling the temperature at 30-40 DEG C and maintaining the temperature for 1-3 hours, wherein the parts by weight of plant lactobacillus, the phosphate solubilizing bacteria, the potassium solubilizing bacteria, the bacillus subtilis culture, the aspergillus awamori culture and polyglutamic acid are respectively 20-35 parts, 1-2 parts, 2-4 parts, 10-15 parts, 8-15 parts and 5-8 parts. The fertilizer can be used for enhancing the drought resistance capabilities of crops, improving the physical properties of soil, improving the use efficiency, regulating acid-base balance of soil and reducing pollution of harmful substances in soil, such as nitrite and is conductive to increasing soil fertility.