<p>AP/HTPB/Al propellant is a commonly used propellant in solid rocket engines. Measuring the free radicals generated during combustion through atomic emission spectroscopy is a common method for studying the combustion characteristics of propellants. Based on previous experimental studies, it was found that NH₂ radical signals sometimes appear and sometimes disappear in spectral measurements, and this study experimentally and numerically investigates this peculiar phenomenon. Spectral and temperature measurement experiments, as well as reaction kinetic combustion numerical simulations, were conducted on the AP/HTPB/Al propellant to analyze the behavior of NH₂ free radicals during the combustion process of the propellant. Firstly, it was discovered through a fiber optic spectrometer that the appearance of NH₂ in the combustion process of three-component propellants is accidental, consistent with previous studies. A reaction kinetic combustion model for AP/HTPB/Al three-component propellants was established, and the behavior of NH₂ radicals during combustion was analyzed through reaction kinetics. And through this model, the temperature, combustion products, and intermediate products of aluminum-based composite solid propellants were obtained over time, and the role of NH₂ in the combustion process of propellants was discovered: determining the oxidizing atmosphere of the propellant composite and promoting the oxidation process of aluminum. Through model analysis, it is speculated that increasing the content of NH₂ is beneficial for the smooth combustion of aluminum in propellants, and simulation calculations were conducted to verify this hypothesis. This study is of great significance for understanding the combustion process of aluminum-based composite solid propellants and adjusting the propellant formulation.</p>