Abstract: Performance degradation of a long lifetime "Oxford" style stirling cryocooler is mostly traceable to internal contamination, so it is important to understand outgassing property of material used. In this paper, outgassing characteristics of six key internal material are tested, and the main contaminants are water, hydrocarbon, phthalate and so on. Based on nonmetal material outgassing theory, the outgassing characteristic model is established. It is benefit and valuable to select key internal material, to optimize outgassing techniques, as well as to control contamination failure mode.