Abstract: A new role base access control (RBAC) based authentication model which can resolve virtue organization (VO) authentication problem in large scale is proposed. The new model provides security to grid system in two aspects:firstly it makes user management and authentication more precisely, secondly, it reinforces authentication strategy at local level. According to the characters of VO in the Grid, we need a new solution to relieve burden of security, hence the optimized authentication architecture is built to achieve the better performance as well as reduction of total cost of ownership.