The invention discloses a method adopting a combined technology of pre-oxidation and coagulating sedimentation to process wastewater containing thallium and ammonia-nitrogen. According to the method, a sodium hypochlorite oxidizing agent is added into a wastewater collecting tank so as to oxidize metal ions in wastewater, the monovalent thallium is fully oxidized into trivalent thallium, monovalent thallium is converted into complex under the effect of strong oxidant, and at the same time, the nitrogen in ammonia-nitrogen is degraded and removed in the form of nitrogen gas. After pre-oxidation, the wastewater is lifted to an integral processing facility through a self-sucking pump; ferrous sulfate and poly aluminum chloride (PAC) are added to form alumen ustum flocculus in a precipitation unit, the precipitate is wrapped, the thallium complex is adsorbed, then quicklime is added to adjust the solution to an alkaline environment; in the alkaline environment, Fe<3+>, Al<3+>, and prepolymer products thereof carry out hydrolysis quickly to form Fe(OH)3 flocculus and Al(OH)3 flocculus; before the flocculus becomes big, the adsorption sites on the surface of flocculus form covalent bonds with Ti<3+>, the flocculus becomes bigger and bigger very quickly and goes on absorbing Ti<3+> in water; at the same time, Ti<3+>, Fe<3+>, Al<3+>, Zn<2+>, lead, and cadmium carry out co-precipitation reactions, and thus the heavy metal ions in water are removed.