Northward indentation of the Qaidam Basin (QB) and southward underthrusting of North China Craton (NCC) lithospheric mantle beneath the Qilian Shan (QLS) are two frequently-cited geodynamic modes for interpreting the evolution of the northeastern Tibetan Plateau. We here aim at understanding the roles of these two dynamic processes in crustal deformation and how they interact during plateau growth in the NE margin by using sandbox experiments that simulate the convergence of the QB-QLS belt through indentation and underthrusting type of boundary conditions individually, alternately or synchronously. Results illustrate that 1) Underthrusting beneath the QLS favors a gently-tapering, one-sided thrust wedge only above the downgoing slab. 2) Indentation of the QB promotes the occurrence of doubly vergent convergent belts with two oppositely-tapering thrust wedges spreading from the slab boundary. 3) Diverse convergence histories lead to distinct deformation patterns for the modelled convergent belts. However, only when indentation and underthrusting occurred synchronously, the modelled thrust wedge resembles current QB-QLS belt in terms of growth sequence, wedge geometry and deformation localization pattern, indicating that bidirectional compression mode maybe the best approximation for the late Cenozoic northeastern Tibetan Plateau. Our experiments further reveal that shift of boundary conditions like alternation of geodynamic drivers and encountered foreland buttress, would result in limited changes in uplift rate of individual structures. Instead, switch between different structural evolutionary stages causes more pronounced variations and should be noted when interpreting thermochronologic data from the northeastern Tibetan Plateau.