The invention relates to a polyacrylate modified water-based enclosed isocyanate curing agent and a preparation method thereof. The curing agent is obtained by neutralizing and emulsifying a prepolymer formed by polyisocyanate semi-enclosed object and hydroxyl-containing polyacrylate, and the mole ratio of NCO to OH is 1-1.15:1. The hydroxyl-containing polyacrylate is prepared by: taking 10-50wt% of a solvent as the base material, and dripping a mixture composed of 5-15% of a carboxyl-containing vinyl monomer, 2-20% of a primary hydroxyl or secondary hydroxyl-containing acrylate monomer, 1-10% of a primary hydroxyl-containing epsilon-caprolactone modified vinyl monomer, 5-70% of other monomer containing a vinyl structure, 0.1-5% of a chain transfer agent and 0.05-3% of an initiator into the base material. The sealant and polyisocyanate for preparation of the polyisocyanate semi-enclosed object are in a mole ratio of 1.05-1.5:1. The curing agent has good miscibility with the matrix resin, high curing efficiency, low cost, flexibility and impact resistance.