To study the mechanical properties of polyvinyl butyral(PVB)-based high solid content propellant, the effect of PVB with various viscosity, PVB blended with viscosity of 45 mPa·s and 300 mPa·s and plasticizers 1, 2-dibutylphthalate (DBP) and acetyl tributylcitrate (ATBC) on the PVB-based high solid content propellant was analyzed by a static mechanical test. The effect of PVB with various viscosity and two plasticizers on the dynamic mechanical property of PVB-based propellant was studied by dynamic thermomechanical analysis (DMA). Results show that with the increase of the viscosity of PVB, the high temperature tensile stress of the propellant increases, the normal temperature and high temperature elongation decrease. The PVB blended with mass ratio of 1:3 with viscosity of 45 mPa·s and 300 mPa·s can make the tensile mechanical properties of the propellant achieve the average value of these two kinds of single viscosity propellant. Replacing DBP with ATBC decreases low and normal temperature tensile elongation slightly The PVB based propellant with PVB of viscosity of 45 mPa·s has stronger α-transformation and the propellant with plasticizer DBP has stronger β-transformation.