The invention discloses an environment-friendly clay stabilizer. The environment-friendly clay stabilizer comprises, in parts by weight, 5-30 parts of a benzyl quaternary ammonium salt, 10-30 parts ofa heterocyclic polyquaternary ammonium salt, 35-40 parts of a sulfonyl quaternary ammonium salt and 5-40 parts of choline chloride, wherein the benzyl quaternary ammonium salt is prepared through a reaction among N-aminoethyl ethanolamine, formaldehyde and benzyl chloride, the heterocyclic polyquaternary ammonium salt is prepared through a reaction among N-aminoethyl ethanolamine, formaldehyde and dichlorodiethyl ether, and the sulfonyl quaternary ammonium salt is prepared through a reaction among diethanolamine, formaldehyde, diethyl sulfate and bis(diethanolamine) methane. The clay stabilizer has a wide pH application environment, high temperature resistance and high anti-expansion performance at the same time, is suitable for various downhole working liquids with pH values of 1-14, andhas resistance to a high temperature of 150 DEG C, an anti-swelling rate of larger than 88% and an anti-swelling performance duration time of more than 1 month, and it is verified through biocompatibility experiments that the semi-lethal concentration LC50 of the clay stabilizer is larger than 10000 mg/L; and therefore, the clay stabilizer has excellent environmental protection, and is suitable for an additive for preparation of fracturing fluids, acid solutions, perforating liquids, workover fluids and other types of downhole working fluids.