Ongoing commissioning is important for improving the energy efficiency of large scale air conditioning systems. It should be an essential part of building operation and maintenance. However, normal ongoing commissioning is timeconsuming and needs expert experience. This paper therefore presents a quick, streamlined ongoing commissioning method. Based on operation data logs stored by building management systems (BMS), this method can give primary evaluations on system performance and supply suggestions for operation optimization and equipment retrofit. This method has been appliedin a shopping center in Hong Kong. The applications have been introduced in detail as examples to illustrate the method.