The invention discloses a soil curing agent and a preparation method thereof. The soil curing agent comprises potassium chloride, sodium chloride, calcium chloride, magnesium chloride, ammonium chloride, citric acid, sodium tripolyphosphate, calcium oxide, calcium hydroxide, aluminum oxide, sodium hydroxide, sodium carbonate, calcium sulfate, potassium sulfate and silicon dioxide. The preparation method comprises the following steps: weighing raw materials, and uniformly mixing; conveying the raw materials into a mixing cabin of a specific mixing machine through a spiral feeding conveying machine, and stirring different raw materials so as to obtain a mixed material; conveying the mixed material to a finished product cabin through a discharge spiral conveying machine, thereby obtaining a finished product of the curing agent. By adopting the soil curing agent, soil caking is accelerated, the connection strength of soil granules is improved, the strength of a soil body and the water stability of the soil body are improved, and the cost of the soil curing agent is reduced.