Preparation method for C.I. pigment red 176

The invention provides a preparation method for a C.I. pigment red 176. The method comprises the following steps: directly grinding 5-(2'-hydroxyl-3'-naphthamido)-2-benzimidazolone with a colloid grinder without the need of dissolving, and adding an emulsifier and carrying out pulping; then adding diazonium salt and carrying out reaction, and carrying out coupling and controlling a pH value of a reaction system by using alkalescent water at the same time so as to guarantee smooth reaction, reduce decomposition of diazonium salt and dissolved state of coupling components, improve reaction efficiency and yield and enhance product quality; and finally, directly adding a solvent into a prepared crude filter cake without the need of drying treatment, and carrying out pigmentation treatment so as to prepare the C.I. pigment red 176. The C.I. pigment red 176 has the advantages of uniform particle size, flabby and soft particles, excellent dispersity, bright color and high tinting strength.