Services computing is an interdisciplinary subject that devotes to bridging the gap between business services and IT services. It is recognized that Requirements Engineering is fundamental in implementing the service oriented architecture. It takes traditional RE techniques great efforts to model business requirements and search for the appropriate services. In this paper, we propose an ontological approach to facilitate the service-oriented modeling framework. The general idea is to establishing a common semantic language to describe both the business requirements and services capabilities based on their effects on the environment. After that, we used a case study to illustrate this method and showed that substantial efforts can be spared to construct a service model from business requirements.