Abstract: A model was developed to analyze the inter-filament mechanical function,and the creep of the cross section PTT and PET filaments was expatiated by four element models.The mechanical parameters of the filaments such as elasticity module and viscosity coefficient were got,which were used to validate the stress slack of the filaments,showing in good accord with the macro performance of the filaments.It can be seen that the four element models can be applied to character exactly the mechanical properties of the filaments in theory.It can describe the rapid elasticity and slow elasticity of the filaments and verify their creep,and is advantageous over the three element models.