The invention discloses a composite curing agent suitable for peat soil and a preparation method thereof, and belongs to the field of civil building materials. The composite curing agent suitable forpeat soil is made from 100-300 parts of cement as a self-setting material, 70-150 parts of red clay as pore filling, particle dispersion and organic dilution components, 10-30 parts of phosphogypsum as an alkaline excitation component, 3-9 parts of sodium sulfate, 1.5-4.5 parts of sodium chloride as a hydration acceleration component, and 300-400 parts of water as a hydration inducing component. The curing agent can significantly improve the strength of peat and peaty soil, and the performance of the peat and peaty soil as a building foundation and a roadbed filler is optimized. The consumption of cement for curing peat soil is reduced, the red clay is easy to obtain from local sources, the utilization of waste soil in engineering is improved, and the use of phosphogypsum can reduce the environmental pollution caused by phosphogypsum stacking. The raw materials of the composite curing agent are easy to obtain, the preparation is simple, the cost is low, and the curing agent has certainenvironmental and economic benefits.