The invention discloses a sodium alginate-based pH-responsive drug microcapsule, which comprises the following components in parts by weight: 8-12 parts of a hydrophobic vinyl monomer, 0.6-1 part of a cross-linking agent containing a double bond, and a hydrophobic drug 1-2 parts, 3-5 parts of sodium alginate monomer, 0.06-0.1 parts of hydrophilic surfactant, 0.3-0.5 parts of initiator, 20-30 parts of oil-soluble drug solvent and 338-563 parts of water. The preparation method includes: a) weighing each component; b) dissolving hydrophobic vinyl monomer, double bond-containing cross-linking agent and drug in an oil-soluble drug solvent to obtain an oil phase; c) dissolving sodium alginate 1. The surfactant is dissolved in water to obtain a water phase; d) Add the oil phase to the water phase and emulsify to obtain an oil / water emulsion; e) After the oil / water emulsion is heated up, add an aqueous solution of the initiator dropwise, and after the reaction, centrifuge , washing and drying to obtain microcapsules. The preparation method provided by the invention is simple, easy to operate and has good reproducibility, and the prepared microcapsules have small particle size, uniform distribution, high encapsulation rate, good wall material mechanical properties and stable drug release performance.