NEPE propellant has been exposed to different temperature and humidity environment. Mechanical properties,gel fraction and content of stabilizers have been measured to investigate humidity-heat combination aging characteristic of the propellant. Results show that the humidity-heat aging of NEPE propellants is expressed as a combination of physical aging and chemical aging. The physical aging is in character of humidity aging: mechanical properties change rapidly at first and then slowly as time extending,finaly trend to fixed values. The chemical aging is in character of heat aging: there is a plateau of mechanical properties at the beginning,then a rapid drop succeeds to,and a low plat roof appears in the end. There are cooperative effects in humidity-heat combination stress aging: humidity accelerates chemical aging,and temperature increases depth and velocity of the physical aging. The basic chemical characteristic of heat-humidity aging of NEPE propellants is similar to that of heat aging. But humidity accelerates the depletion of stabilizers and the decomposition of binder network. Namely,humidity decreases apparent active energy of heat aging.