The combustion performance of gun propellants containing FOX-7 at low pressure was studied by quenched burning tests and closed bomb tests. Results show that the pressure exponent reduces with increasing of the content of FOX-7 in propellant, and consecutive melted layer on propellants surface formes during combustion process. It restrains the deflagration of RDX, and the combustion consistency of propellant better, which is helpful for the stable combustion of propellant at low pressure. Impact test results indicate that with the increasing of FOX-7 content in formula, impact strength of propellants improves significantly.