The invention relates to online fracturing fluid and a preparation method therefor. The online fracturing fluid contains the ingredients in parts by mass: 0.8-5 parts of agent A, 0.2-1 part of agent B and 94-99 parts of water; the agent A contains the ingredients in parts by mass: 10-20 parts of chitin, 10-20 parts of starch, 5-20 parts of acrylamide, 2-5 parts of bioactivator, 0.1-1 part of sugar, 0.1-0.5 part of sodium polyaspartate, 10-20 parts of environment-friendly solvent and 13.5-62.8 parts of water; and the agent B contains the ingredients in parts by mass: 5-20 parts of alkaline proteinase, 10-20 parts of bioactivator, 5-10 parts of EDTA-4Na, 0.1-0.2 part of sodium ethylenediamine disuccinate, 0.5-1 part of sodium polyaspartate, 0.2-1 part of sodium acetate, 0.5-1 part of sodium lactate, 0.5-1 part of potassium lactate, 0.5-1 part of sugar, 5-10 parts of ethanol and 34.8-72.7 parts of water. The online fracturing fluid has the characteristics that online continuous preparation is achieved, the operation is simple, the working concentration is low, the viscosifying speed is high, the sand carrying performance is good, the friction drag is low, the damage is low, the online fracturing fluid is heat-resistant and shear-resistant, the viscosity of flowback fluid is low, the applicable range is wide, the cost is low, the production increase effect is good, and the like.