The invention relates to a modifier for a high-liquid-limit clay pavement. According to the modifier, the basic principle is that a series of physical and chemical reactions of inorganic binders and high-liquid-limit clay are utilized, the liquid limit and the plastic index of the high-liquid-limit clay are reduced to the maximum degree, the unconfined compressive strength and the CBR strength areimproved, and the requirement for the performance of the high-liquid-limit clay pavement in the specification is met. The modifier for the high-liquid-limit clay pavement is prepared from the following raw materials in parts by weight: 107-143 parts of flue gas desulfurization gypsum, 95-122 parts of phosphogypsum, 88-117 parts of red mud, 66-158 parts of lime and 380-460 parts of pulping white mud. According to the modifier, the doping amount of the modifier in the using process is 10-15% of the mass of dry clay, the liquid limit of modified clay is 45-53%, the plastic limit is 33-40%, the plastic index is 13-19, the 7d unconfined compressive strength of the modified clay is 0.4-1.0 MPa, and the soaking 4d CBR strength is 10-20%. The modifier has the advantages that multiple industrial solid waste compound modification is adopted, so that the high-liquid-limit clay is modified from standard waste clay which is not allowed to be used into a roadbed filler capable of being utilized, meanwhile, the construction performance and strength of the high-liquid-limit clay are improved, and the construction cost is lowered.