Methods of increasing the oxygen balance of singlebase propellant were studied. The oxygen balance,flame temperature,explosion heat,specific energy and gas component were calculated by the minimum free energy method. The calculated results show that the total amount of combustible gases in the propellant combustion products,contents of H₂,CO and CH₄ decrease with the increasing of ammonium nitrate content. When the content of ammonium nitrate is more than 80%,the combustible gases are completely oxidized to carbon dioxide and water. Experiments were performed on a mixture of one served propellant of some gunlaunched missile with propellant containing ammonium nitrate. Results show that when the content of ammonium nitrate propellant is 50%,the oxygen balance is increased by 39.2%. It reveals that the content of CO in combustion products is decreased by 32.8%,while integral optical density(IOD) is reduced by 36.4% by analyzing the photographs of gun muzzle flame.