In this study, the effect of the intake plenum design on the scavenging process in a newly proposed 2-stroke Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) engine was studied in detail by three dimensional (3D) computational fluid dynamics (CFD) simulations. In the BUSDIG engine, the intake scavenge ports are integrated into the cylinder liner and their opening and closure are controlled by the movement of piston top while exhaust valves are placed in the cylinder head. In order to accommodate the optimized scavenge ports in the real engine application, the intake plenum with an inlet pipe and a scavenge chamber was designed and connected to the 12 evenly distributed scavenge ports in a single cylinder BUSDIG engine. In order to achieve optimal scavenge performances and sufficient in-cylinder flow motions to enhance the fuel/air mixing, five design parameters of the intake plenum were investigated, including the ratio of the inlet area relative to the scavenge port area (rI/S), the radius of the round connecting the inlet pipe and the scavenge chamber (rR), the ratio of the scavenge chamber volume to the cylinder displacement volume (rS/C), the angle between the inlet pipe and exhaust pipe (αI/E) and the ratio of bore to the scavenge port length (rB/PL). It is found that the best scavenging performance is achieved at low engine speed when the intake plenum design shows less impact on the scavenging performances. As the engine speed increases, the impact on the scavenging performance by the intake plenum design becomes more significant. There is a trade-off between the tumble ratio (TR) and cross tumble ratio (CTR) for each intake plenum design. Based on the systematic study carried out, the intake plenum design parameters were optimized for high scavenging performance and strong large scale flow motions in the BUSDIG engine.