Building Commissioning is a rapidly growing building engineering and managerial practice towards building energy efficiency. It is being the hot topics and one of those building energy services receiving frequent requests from building owners in recent years because of its benefits in improved project delivery results. This paper introduces the purpose, working process, potential technologies, findings and solutions by presenting a real world large scale commercial project case study. Through the actual outcomes of this Commissioning project, it is proven that Commissioning is a very promising and also could be no cost/low cost energy conservation measure, which can bring surprisingly good return to the building owner, occupant and operation & management team.