The diffusion of deterrent in manufacturing process determines the interior ballistic performance of newly manufactured extruded impregnated propellants. The diffusion of polymeric deterrent was investigated by FTIR microspectroscopy. The results show that the concentration profile of deterrent of newly manufactured propellant is in accord with the Second Fickian diffusion model. The diffusion coefficient of deterrent in manufacturing process can be calculated by the concentration profile equation,which is 1.639×10^-13 m²·s^-1. A comparative experiment was carried out between internal standard method and external standard method. The results show that in the internal standard method the mathematical treatment of uniform distribution of NG in deterred layer has no effect on the order of magnitude of the diffusion coefficient,so the systematical deviations of the reconcentration profile obtained from the imperfection of calibration model can be neglected.