Shear links is a kind of commonly used energy dissipation component of which the yield force is always multiplied by a hardening factor to check the capacity of gusset plates and embedded parts or other connecting components. If the overstrength fact due to hardening is underestimated, there are safety hazards. In this paper, three tests on I-shaped shear links with the LYP100 steel web are carried out. The specimens are designed with three extremely small length ratio to expand the range of existing data. Through the finite element analysis model, the contribution of the flange to the shear force of the links is further studied, and a schematic diagram of the theoretical study is given. Based on the parameters of the material combined hardening model, an analytical model formula for evaluating plastic overstrength and calculating lower bound and upper bound of plastic hardening is proposed. The orthogonal finite element analysis of five geometric parameters (web thickness, length of link, flange width , flange thickness , web plate height) is conducted for obtaining the overstrength factors and determining the parameters of the analytical method. The method and formulas are assessed, showing satisfactory accuracy.