Method for preparing pigment red 5

The invention provides a method for preparing pigment red 5. The method for preparing pigment red 5 comprises the following steps: (1) preparation of red base ITR diazonium salt; (2) dissolution of coupling component naphthol AS-ITG; (3) coupling: parallel flow coupling, i.e. the red base ITR diazonium salt obtained in Step (1) and naphthol AS-ITG (2',4'-dimethoxy-5'-chloro-2-hydroxyl-3-naphthanilide) dissolved solution are simultaneously added into a base solution; (4) post treatment of pigment. According to the method for preparing C.I. pigment red 5 disclosed by the invention, core spun phenomenon is generated by using acid separation or coupling through adding a surface treatment agent fatty acid methyltaurine sodium salt when the coupling component naphthol AS-ITG is in alkali dissolution; the yield is improved and coupling is promoted by adding 2,4,6 tri-(1-phenethyl)-phenol polyethylene glycol ether with 8-30 EO so as to catalyze reaction speed and prepare high-performance P.R.5 with a high synthesis rate.