We have studied concerning the design technique of ankle-foot orthosis (AFO) that is used spastic hemiplegia of the stroke. We developed the equipment for measurement in order to measure the influence which it causes to spasticity gait. The ankle joint moments are calculated by the measurement data. In addition, you appraised of gait lability as the scatter plot by the angle and the moment of ankle joint in heel contact. These appraisal results were made the element which selects the orthosis. The design of the orthosis was utilized three dimensional cad, and the structural of the orthosis was analyzed the non-linear finite element analysis by the boundary condition which utilizes the measurement data. In this study, the life prediction of the orthosis which deals with 2 orthosis users was made help of the design factor. In order to investigate the life cycle of the orthosis user, the number of steps and living conditions were investigated. As for material definition S-N curve of the PP material was used. The result of fatigue analysis, it was suggested that fatigue analysis of the orthosis is effective as the help in orthosis designing.