In our previous study, diffuse slip line (DSL) yield mode without an inhomogeneous deformation, local shear band and necking, has been found by in-situ observations of simple shear deformation for glassy polyethylene terephthalate (PET) under the conditions of low strain rates and high temperatures. Growth process of DSL can be formulated as a thermally activated process, that is, Eyring's flow model. The growth rate and density of DSL increase with increasing stress and strain, respectively. Plastic deformation proceeds by molecular process which activated segments of polymer chains exchange their positions with free volume under applied shear stress. In the present study, several parameters necessary for an empirical simulation of stress-strain curves, that is, activation parameters, variation rate of DSL length with stress, and variation rate of DSL density with strain have been determined experimentally. Using these parameters, stress-strain curves are culculated by an analogical analysis to Johnston-Gilman’s mathematical method for the yield of metals.