The invention discloses a synergist for soil acid acidification, and a preparation method and a use method thereof. The synergist is prepared from, by mass, 25-38% of a barium sulfate strontium scalesolubilizer, 18-25% of a polycarboxylic acid dispersant, 5-15% of a penetrant, 12-20% of a mutual solvent, and the balance of water. The raw materials in the formula are environment-friendly, non-toxic and harmless, and a small amount of synergist for soil acid acidification is added to a conventional solonic acid solution system to quickly complex with calcium ions, barium ions, iron ions and thelike after an acid liquid reaction, so the solubility product of barium sulfate is improved, dissolution of barium sulfate is achieved, the inhibition performance of acid liquor on secondary precipitation of calcium fluoride, fluoroaluminate, ferric hydroxide and the like is effectively improved, expanded clay mineral crystal lattices are distorted and dehydrated, and blocked stratum pores are recovered. The synergist for soil acid acidification can effectively solve the damage of secondary precipitation caused in the conventional soil acid acidification process to stratums.