The invention belongs to the field of metal material performance detection, and particularly relates to a detection method for the strain hardening index n value of a metal material. The detection method includes the following steps that a, the strain hardening index no value, yield strength delta so and tensile strength delta bo of a metal standard part of a kind of steel are measured; b, the strain hardening index no value, yield strength delta so and tensile strength delta bo are substituted into the formula (I) shown in the specifications, so that the C value of the metal material of the kind of steel is obtained; c, the yield strength delta s and tensile strength delta b of the part, to be tested, of the kind of steel are measured; d, the delta s and delta b values measured through the step c are substituted into the formula (II) shown in the specifications, so that the n value of the metal material is obtained through calculation. The new corresponding relation between the n value and the yield ratio of the material is provided, precision is high, and the method is simple, easy to implement, efficient and rapid, can reduce the workload of detection in a steel factory substantially, and has innovation and breakthrough.