This paper describes reliability assessment from measured data of double-stress accelerated degradation test which taking functional unit as research object. Most of performance degradation reliability analyses pay attention to components. Thereby assessments are relatively easy because they have simple function and clear failure mechanism. However, in reality, functional units compose system, and the reliability of a functional unit is affected by all of the jointing components synthetically which puts up a unitary degradation process. On this consideration, double-stress uniformly orthogonal accelerated test is putting on the whole board of functional units under temperature and relative humidity stresses (80 degC,55%), (100 degC,25%), (90 degC,85%), (110 degC,65%). Accelerated test design is introduced in this paper and the collected measured degradation data are shown by figures. According to statistical analysis reliability information is inferred from test data and assessment result is compared to results educed by other methods. Conclusion is result gain by this present way and is basically consistent with other studies. Functional unit reliability assessment based on performance degradation data is feasible and reliable.