Accelerated degradation tests (ADTs) are often applied for assessing the reliability of highly reliable products, but it is realized that ADT experiment can also be used as a tool for improving product design. In particular, when external stress factors are not constants in a product's use environment, it is necessary to utilize ADT experiments to investigate the interaction between these stress factors and product design factors so that a robust design, which is insensitive to external stress factors, can be obtained. In this paper, a methodology is developed for achieving product robust design via ADTs. We present a degradation model that can be used for studying the effects of design and stress factors on degradation rate. Model parameter estimation is obtained by the maximum likelihood method and an optimization procedure is derived for finding the best setting of design factors that can minimize the effect of stress variation. Finally, the proposed method is validated by a case study of window wiper switch experiment.