The invention provides a preparation method of a concrete inner curing agent with a core-shell structure. The preparation method comprises the following steps: preparation of a core material, preparation of a shell solution, and preparation of the concrete inner curing agent. The step of preparation of the core material comprises: uniformly mixing cyclohexane and a suspending agent to obtain an oil phase; uniformly mixing acrylic acid, sodium hydroxide, a cross-linking agent, an initiator and water to obtain a water phase; heating the oil phase to 40-60 DEG C; adding the water phase drop by drop; performing a polymerization reaction for 1-4h; and drying the resultant to obtain the core material. The step of preparation of a shell solution comprises uniformly mixing polyhydric alcohol, aluminum sulfate, an epoxy compound, a catalyst and water to obtain a shell solution. The step of preparation of the concrete inner curing agent comprises: spraying the shell solution onto the surface of the core material; performing uniform mixing; and performing a heating reaction to obtain a final product. According to the invention, the preparation method is simple; the chemical structure is easy to control; the obtained concrete inner curing agent with the core-shell structure can greatly improve the moisture content of the inside of concrete, and has an obvious effect on self-constriction and shrinkage of early concrete; and the problem that the early concrete cracks is solved.