The surface properties of AP with various particle sizes and nitrocellulose (NC) with various content of nitrogen, and the interface properties between NC and AP were studied by using the dynamic contact angle and interface tension technique. And the effects of the surface and interface properties on mechanical properties of Composite Modified Doublebase Propellant Containing AP and Aluminium were also investigated. It was shown that the surface energy of AP increases with the increase in its particle size, while the surface energy of NC increases with the increasing nitrogen content of NC. At the same time, the particle size of AP plays a key role on the interface energy and adhesion energy between NC and AP, and the interface energy and adhesion energy decrease with decreasing particle size of AP. But the effect of interface energy decreasing on mechanical properties of the propellants is higher than that of adhesion energy, and the higher tensile strength of propellant is obtained when particle size of AP decreases. In addition, as the nitrogen content of NC decrease, the interface energy between NC and AP decrease and corresponding adhesion energy increase. The high tensile strength of corresponding propellant is also obtained herein.