To investigate the evolution of the internal structure and mechanical properties of double-base flake gun propellant during pressing， samples from four typical processing stages—raw materials， thin pressing （1， 3， 5， and 7 passes）， thick pressing （1， 3， 5， 7， and 10 passes）， and finishing pressing （1 and 2 passes）—were systematically characterized. A combination of analytical techniques， including scanning electron microscopy （SEM）， micro-computed tomography （μ-CT）， Fourier transform infrared spectroscopy （FTIR）， tensile testing， dynamic mechanical analysis （DMA）， and linear expansion coefficient measurements， was employed to elucidate microstructural evolution， component interactions， and macro-property variations under thermomechanical coupling. The results indicate that thin pressing constitutes the main dehydration phase， reducing the water content from 22.6% to 0.46% and increasing the density from 1.474 g·cm^-3 to 1.611 g·cm^-3. At this stage， the nitrocellulose （NC） fibrous framework becomes clearly visible， and initial plasticization occurs. Thick pressing is identified as the critical period for plasticization， during which nitroglycerin （NG） molecules penetrate between NC molecular chains， disrupting the original hydrogen-bond network and forming new intermolecular interactions. This process significantly enhances the elongation at break to over 50%， eliminates internal pores and defects， and results in a homogeneous and dense structure. In contrast， fine pressing mainly serves to adjust the propellant sheet to its final thickness， with no notable changes in internal structure or fundamental mechanical properties.