Abstract: Solid-state polymerization (SSP) is one of the important methods to synthesize high quality and high molecular polyesters and polyamides for tyre cords and engineering plastics.A theoretical model describing the kinetic behavior of the SSP of Nylon 6 with bifunctional acid regulator is presented based on some hypotheses,and verified by the experimental data of the authors for the SSP of spherical pellets of Nylon 6.This model consideres the effect of segmental diffusion on reversible step growth polymerization and small molecule water diffusion.The simulation results show that reaction temperature and time and water content is three important factors and that number-averaged molecular mass increases with increasing reaction temperature and time in the experimental ranges of the SSP of Nylon 6.It is in agreement with the mechanism of postcondensation in the SSP.