The influence factors of slow cook-off characteristic of solid propellant were studied with the object of HTPE propellant and GAP propellant by means of slow cook-off experimental device and thermocouple and pressure transducer, including composition, burning rate, heating rate, restriction condition, and free volume. HTPE propellant has a very excellent slow cook-off characteristic, hut the addition of HMX increases the response extent of slow cook-off, and free volume has not obvious effect on the response extent of slow cook-off. The burning rate from 10.1 mm·s^-1 to 32.2 mm·s^-1 and the heating rate from 3.3 ℃·h^-1 to 1 ℃·min^-1 have scarcely effect on the response extent of slow cook-off characteristic of GAP propellant. The response extent of slow cook-off becomes more violent after increasing restriction condition for HTPE propellant and GAP propellant.