Nylons are widely used as engineering plastics. When used as packaging materials for power system chips, the aging of nylons in the natural environment may cause package failure, reliability deterioration of chips, or even chip failure, and finally, lead to great loss in the power industry. Therefore, aging evaluation of nylons has attracted great attention. Conventional aging evaluation methods include natural weathering and artificial accelerated aging. Both of these two methods are time-consuming. Furthermore, the effects of various environmental factors on aging of nylons can not be investigated. In this paper a novel in-situ aging evaluation method was proposed and the corresponding system was developed to study nylon 6 (PA6) and nylon 66 (PA66)’s aging stability. The system can combine environmental factors such as irradiation, temperature, humidity and oxygen. By measuring the generation of gaseous degradation products during aging process of nylons, the stability can be compared. The results show that the gaseous degradation products of PA6 and PA66 are mainly H₂O and CO₂, and CO₂ is used as an indicator to evaluate the aging status. Nylons with different natural pre-aging times were detected. Longer pre-aging time responds to more generations of CO₂, demonstrating poorer stability. Furthermore, this method was applied to study the effect of humidity on the aging of PA6 and PA66. It was proved that humidity accelerates nylon aging, and high temperature further promotes this acceleration effect. The novel in-situ aging evaluation method can evaluate aging stability of nylons under versatile environmental factors in only several hours. It is also expected to be a powerful and promising aging evaluation method for other polymer materials.