Requirements engineering in a system-engineering project is a key factor in the success of a project. In the current state, stand-alone research has been conducted tackling this area, however, few studies addressed the requirements based on a probabilistic approach. In this thesis, a multi-scale probabilistic approach has been developed, named Bayesian Network, to evaluate the requirements engineering of a complex systems In order to pursue the aim of this paper, the FFG(X) navy ship is chosen to serve as a case study and to validate the proposed model. Results indicate the sub-requirements that highly affect the FFG capability/performance. These sub-requirements are: 1) guns, 2) ballistic missiles, 3) antisubmarine, and 4) radar.