GAP modified double-base powder was prepared by an internal solution method and applied in cross-linked modified double-base propellants. It was found that if GAP content was not more than 30 %, the modified double-base powders had high roundness rate, no bonding between the particles and excellent fluidity. The median diameter (d50) of powders was decreased from 90.24 to 72.41 μm when the amount of GAP increased from 0.0 to 30.0 %. The thermal decomposition peak temperatures of –N3 and GAP’s main chain were found to be lower for the 10.0, 20.0 and 30.0 % GAP modified powders than the corresponding peak temperatures for pure GAP. The drop mass impact sensitivity of the modified powders is reduced as the mass ratio of GAP increases. It was experimentally shown that GAP modified double-base powders can improve the mechanical characteristics of the propellant with a maximum tensile strength (σm) between 0.45 MPa < σm < 1.18 MPa and an elongation at maximum tensile strength (em) between 29.80 % < em < 52.60 % at temperatures of −40, +20 and +50 °C.