Service sector in the US contributes a high proportion of GDP, four out of five people work in services. It is important to enable service firms to make the most out of the domestic and the international opportunities. Services focus on the project based Six Sigma application and selecting the critical quality factors and business strategies to improve key performances and retain competitive advantages in the globe. However, the service sectors and its surroundings becoming more and more complex, it is simply not possible to solve all the problems and improve key performances given the limited resources. The purpose of this study is to develop a model that provides a systematic evaluation to identify the key quality factors and potential business strategies to enhance the effectiveness of service performance. Deriving from the Bayesian Network methodology, the proposed model combines a graphical approach to represent relational attributes and variables of interests. The probabilistic inference is made to estimate the likelihoods of the variable aiming the process improvement. The developed model can be used to assess the prioritizing efforts towards the critical business success and key performances associated with Six Sigma initiatives.