The paper aims to design a new type of flame-resistant HDPE plastic box to improve the flame resistance of plastic box for the packaging of gun propellants. The effects of the content and ratio of two kinds of flame retardants, decabromodiphenyl ether and antimony trioxide, on the flame resistance and compatibility of HDPE plastics were inves-tigated by combustion and compatibility tests and the flame resistance mechanisms of the two kinds of flame retardants on HDPE plastics were analyzed theoretically. The test results showed that the flame resistant effect of HDPE plastics without flame retardant modification was poor. With the increase of the content of flame retardant, the flame resistance was improved, and the compatibility was weakened. When the ratio between decabromodiphenyl ether and antimony trioxide is 2∶1, the flame resistance effect is the best; when the content of fire retardant is lower than 11%, the compatibility requirements can be satisfied.