The invention discloses a method for concentrating waste sulfuric acid by utilizing waste heat of a titanium dioxide calcinator, comprising the following steps: at normal temperature and pressure, proper amount of water absorbent is added to titanium dioxide waste acid, liquid water is dissolved out in the form of solid crystal water through the water absorbent, filtrate after solid-liquid separation is cooled, iron vitriol in the solution is crystallized and dissolved out, and the acid liquid is further concentrated; the two steps are repeatedly carried out until the concentration of sulfuric acid in the final filtrate reaches more than 60%, and then the final filtrate is utilized in the acid hydrolysis procedure; and the water absorbent is dehydrated and dried to be regenerated by taking dustproof tail gas of the calcinator, and the steam generated in the drying and regeneration is cooled and flows back to technological process as washing water in titanic acid rinsing or is drained. The method provided by the invention solves the problems of more equipment, long flow and easy blockage in the existing technology, and the equipment investment and operating cost are reduced; and the water absorbent is recycled after being regenerated, so that the energy is saved, the consumption is reduced, and the efficiency is obvious; no wastewater, waste gases and residues are generated in the whole technology, the operability is strong, the productivity of equipment is high, the flow is simple, the investment is less, the cost is low, energy is saved, emission is reduced, and the benefit is obvious.