The development of self-adaptive systems has attracted much attention as they can adapt themselves autonomously to environmental dynamics and maintain user satisfaction. However, there are still tremendous challenges remained. One major challenge is to guarantee the reusability of the system and extend the adaptability with changing deployment environments, or open and complex environments with the existence of unknown. To solve these problems, a conceptual self-adaptive model is introduced, decoupling the environment with the system. This model is a two-layer structure based on internal causes and external causes from the attribution theory. The first layer, determining how the internal causes affect the adaptation behaviors, is independently designed and reusable whiles the second layer, mapping the relationship between external causes with internal causes, is replaceable and dynamically bound to different deployment environments. The proposed approach is evaluated by two case studies, a widely used benchmark e-commerce Web application and a destination-oriented robot system with obstacle and turnover avoidance, to demonstrate its applicability and reusability.