The invention discloses a treating agent for physicochemical treatment on papermaking sewage. The treating agent is prepared through the following steps: uniformly mixing bentonite, starch and coal powder, adding water for pulping, and squeezing into particles with the diameter of 1mm; firing the particles at the temperature of 600-800 DEG C; adding the prepared bentonite particles into an acrylamide aqueous solution, and stirring for 2h with a high speed at the temperature of 40 DEG C; adding cationic monomers at the temperature of 20 DEG C; adding an initiator and raising the temperature to be 45 DEG C to excite a polymerization reaction, raising the temperature to be 85-95 DEG C, then, lowering the temperature to be 60 DEG C, adding a cross-linking agent of which the mass is 0.26-0.63% of that of acrylamide aqueous, raising the temperature to be 70 DEGC, and reacting for 30 min; transferring the system into an environment with the temperature of 105 DEG C, leaving the system to stand and drying, so as to obtain the treating agent for papermaking sewage. The treating agent for papermaking sewage can efficiently adsorb anionic garbage and other pollutants in the papermaking sewage, and can be effectively used for the physicochemical treatment on papermaking sewage.