The thermal decomposition and combustion performance of homogeneous azidonitramine gun propellant composed of nitrocellulose, azidonitramine and nitroglycerine(DA3), azidonitramine gun propellant composed of 85 mass % of DA3 and 15 mass % of RDX(DAR15) and azidonitramine gun propellant composed of 75 mass % of DA3 and 25 mass % of RDX(DAR25) were studied by high-pressure DSC (PDSC) and a closed-bomb. The results show that the DSC curves of DAR15 and DAR25 consist of two exothermic peaks, whereas DA3 gives only one exothermic peak. The first exothermic peaks at 210 ℃ is due to the thermal decomposition of DA3. The second exothermic peaks at 236 ℃ is caused by the decomposition of RDX. With increasing the RDX content, the first exothermic quantity decreases, and the second exothermic quantity increases. In comparison with DA3, the burning rate pressure exponent of DAR15 and DAR25 increases over the pressure range from 40 MPa to 120 MPa and decreases over the pressure range from 120 MPa to the pressure corresponding with maximum dp/dt (p_dpm). RDX makes the initial burning rate and combustion gas generation brisance of DAR15 and DAR25 decrease, and their burning progressivity increases.