Ubiquitous computing environment comprises mobile users, system services, system resource, and sensors embedded into physical environment. The ubiquitous, dynamic, invisible, and open nature of these environments introduces challenging security issues that demand new technical approaches in access control. The exiting access control model for ubiquitous computing environment are lack of context-based authorization mechanism, having redundancy in trust value evaluation and not flexible in role assignment. In this paper, we present a flexible, autonomous and non-redundancy access control model for ubiquitous computing environment which dynamically grants and adapts permissions to users based on context information including time, location and trust value. We specify the authorization mechanism and context evaluation, give the algorithms for the access control model, especially we accomplish dynamic role management.