To optimize the solvent ratio of the coating solution in spraying process of preparing the coating layer of gun propellant with local end-coating flame retardant, the coating solution was prepared using cellulose acetate butyrate (CAB) as desensitized agent, mixture composed of CAB and absorption propellant tablets TG-1 with main components of nitrocellulose and nitroglycerin as solute, ethanol/ acetone of V/V=1/1 as solvent, according to different solvent ratios. Applying the coating solution, the films of coating layers and coated propellants were produced by spraying coating technology. The mechanical strength of the films of coating layers was obtained by an universal material tester. The local amplification observation and analysis of 3D video for surface structure of coating layers before and after tension were performed.The coated propellants were tested by the closed bomb experiments. Results show that the mechanical strength and morphology of both surface and fracture of coating layers are significantly related to solvent ratios. The solvent ratios affect the uniformity and compactness of coating layer materials mainly and are important factor affecting the mechanical strength of coating layers. Thereby, the combustion progressivity of coated propellants is effected.When the solvent ratio is 8:1, the porosity rate is over 95%. At the meantime, the surface of the coating layer obtained is the best smooth, the tensile strength of its film is the maximum, its value is 49.75 MPa, the fracture is the most tidy and the change value in combustion gas dynamic activity for coated propellant achieves a maximum value of 0.0920 MPa^-1·s^-1 in all samples.