The dynamic mechanical properties of NEPE propellant aged for various times at 75 ℃ were measured by dynamic mechanical analysis(DMA). Results show that in the low temperature region, a single relaxation is observed in tanδ-temperature curves, which is glass transition relaxation. The peak value of tanδ and temperature increase with the increase of aging time and test frequency. The effect of the plasticizer contents on tanδ varies with storage aging condition. In seal condition, the tanδ value decreases with the plasticizer content reduction.