In order to investigate the effects of a new energetic photocurable binder terminal acrylate based poly（3-nitratomethyl-3-methyloxetane） （APNIMMO）， on the thermal decomposition and combustion properties of RDX-based photocurable gun propellants， a high-energy APNIMMO/RDX gun propellant sample was designed and fabricated by 3D printing. The thermal decomposition process and related kinetic parameters of the APNIMMO/RDX photocurable gun propellant were studied using differential scanning calorimetry （DSC） and thermogravimetry-differential scanning calorimetry-Fourier transform infrared spectroscopy-gas chromatography （TG-DSC-FTIR-GC）. The combustion performance of the APNIMMO/RDX photocurable gun propellant was evaluated using a closed bomb tester. The results indicate that the thermal weight loss of the APNIMMO/RDX photocurable gun propellant occurs in two main stages. Thermogravimetry and gas product escape mainly focus on the first stage（158.9-234.3 ℃）， In this stage， tthe thermal decomposition of APNIMMO/RDX begins with the exothermic decomposition of APNIMMO， promoting the melting and decomposition of RDX. This causes RDX to decompose earlier， leading to a lower critical explosion temperature （T_pe） for APNIMMO/RDX compared to pure RDX. The second stage （234.3 ℃ to the end of the test） presents a “thermal neutral” state with neither exothermic nor endothermic behavior， mainly attributed to the slow decomposition of the APNIMMO backbone after the complete decomposition of its side-chain nitrate ester groups. The results of combustion performance show that the burning rate coefficient of APNIMMO/RDX propellant is low， the pressure index is high， and there are a large number of holes on the surface of the sample of the aborting combustion test. The analysis shows that in the APNIMMO/RDX propellant system， the burning rate of RDX is higher than that of APNIMMO binder under high pressure due to the large content of RDX. The difference in burning rate between the two causes the heat and pressure generated by combustion to penetrate into the entire propellant along the formed holes， and the process is greatly affected by pressure， so the pressure index is high.