A simulation model was designed for the performance of a single bucket rainwater siphon drainage system and the impact of suspension pipe length. It conducted research on the flow pattern, pressure, displacement, and water level of the drainage system through a simulation operation model and a full-scale experimental platform. Specifically, the model was used to observe the phenomenon of continuous pressure drop at the measuring point under high flow operating conditions, as well as the sudden increase caused by lots of residual air mass passing the measuring point. Meanwhile, a verification method was designed to determine the optimal length of the suspension pipe to optimize the performance of the siphon drainage system. The results showcase that under high flow operating conditions, there is a sudden increase in the overall decrease of system pressure, maintaining maximum flow drainage. In addition, the relative error of the system is 2.35%. When the tail pipe length increases from 0.7 m to 1.1m, the siphon start time increases from 7.38s to 8.21s. The start time of the siphon is positively correlated with the height of the building and the resistance along the system. This achievement has practical guiding significance for the design and improvement of siphon drainage systems.