Abstract: X-ray tangent detection was induced to test the interface between the propellant surface and its coating. The adhesive defect properties of the interface used in free-assemble solid propellant were researched. The optimized investigating condition requirement and the method were found out, and the defect area surface of the interface between the propellant surface and its coating on typical propellant was characterized. The results show that the experiment method is credible and it can be very effective for the quality improving of the solid propellant.