Scour tests on annulus pile-group foundation with cushion caps is of great significance since the stability of the foundation essentially guarantees the structural safety. Limited by test site and model sand selection, the model test requires an extension method for series model to study the local scour at the foundation. The flow regime indicates that wake vortex and lateral flow are main influencing factors of scouring. Tests show that local scour generally happens at both sides of the foundation structure and the backside of water. The scour depth reaches its maximum of 6.01m in extreme high mean sea level (MSL) and decreases as the sea level falls.