Abstract: The power split hybrid electric vehicle (HEV) adopts a power coupling configuration featuring dual planetary gearsets and multiple clutches, enabling diverse operational modes through clutch engagement and disengagement. The multi-clutch configuration usually involves the collaboration of two clutches during the transient mode switching process, thereby substantially elevating control complexity. This study focuses on power split HEVs that integrate multi-clutch mechanisms and investigates how different clutch collaboration manners impact the characteristics of transient mode switching. The powertrain model for the power-split HEV is established utilizing matrix-based methodologies. Through the formulation of clutch torque curves and clutch collaboration models, this research systematically explores the effects of clutch engagement timing and the duration of clutch slipping state on transient mode switching behaviors. Building upon this analysis, an optimization problem for control parameters pertaining to the two collaborative clutches is formulated. The simulated annealing algorithm is employed to optimize these control parameters. Simulation results demonstrate that the clutch collaboration manners have a great influence on the transient mode switching performance. Compared with the pre-calibrated benchmark and the optimal solution derived by the genetic algorithm, the maximal longitudinal jerk and clutch slipping work during the transient mode switching process is reduced obviously with the optimal control parameters derived by the simulated annealing algorithm. The study provides valuable insights for the dynamic coordinated control of the power-split HEVs featuring complex clutch collaboration mechanisms