Existing approaches on reliability assessment of the system entirely depends on expertise, knowledge of system analysts and computation of usage probability of different user operations. Existing approach is therefore can not be taken as accurate, particularly to deal with new or unfamiliar systems. Further modern systems are very large and complex to manipulate without any automation. Addressing these issues, we propose an analytical technique in our work. In this paper, we propose a novel approach to assess reliability of the system using use case model. We consider a metric to assess the reliability of a system under development.