The thermal decomposition and combustion characteristics of nitramine propellants containing N-guanylurea-dinitramide(FOX-12) were studied by DSC-TG, a closed bomb and an interrupted-burning testing instrument. The results show that NC-NG and FOX-12 in the nitramine propellant begin to decompose simultaneously. Adding FOX-12 makes the pressure exponent of the nitramine propellant reduce to less than 1. With the rising of the FOX-12 content, the decline extent of the pressure exponent in the low pressure of 10-20 MPa is larger than that in high pressure range of 40-420 MPa.