Data Warehouses are used to maintain and manage the historical information that is very vital and confidential. Keeping in view the significance of data various data security techniques have been introduced. Most of them consider data security requirements from the early developmental stage of Data Warehouse. In this paper, specific problems related to the existing data security techniques are discussed and a new data security model which is suitable for already developed data warehouses is presented. We implemented this model by using web based application and verified it through different case studies. Key advantages of our approach are reduction of number of access checks that leads to improved data retrieval and reduced analysis time in a secure environment