Ultrasound (US) examination plays a important role in diagnosis process. The goal is to improve the efficiency of US in West China Hospital of Sichuan University. This paper presents results from the use of sub-period appointment. At first, process mapping was used to identify the flow of examination and the bottleneck of it. Then the flow was modeled by the latest simulation platform-simio. Different experiment in simio represent different booking rule, and in different rule we set different time interval. Every experiment has 100 scenarios which have different slots in different periods. Waiting time of patients is seen as performance measures to determine which rule is the best booking rule. Of course, we want to minimize waiting time.