Abstract: By combining rigid underactuated grasping mechanism with compliant mechanism, a multi-mode rigid-flexible underactuated grasping mechanism is proposed, analyzed and experimentally studied.Based on the rigid-body replacement method, the rigid-flexible combination scheme of a two-finger multi-mode underactuated grasping mechanism is designed.Utilizing the forward kinematics analysis and the load equilibrium equation, the static model of the driving unit is established.With the combination of the pseudo-rigid-body model, the load equilibrium equation and the enumeration search for the equilibrium position of operated object, the relationship between the grasping force and the driving moment in the two-point grasping and enveloped grasping modes is modeled.Combining the static modeling of driving unit with that of grasping unit, the complete multi-mode grasping force models can be obtained.Furthermore, the grasping force models are corrected by considering the deformation of flexible linkages induced by contact and using linear interpolation.Based on the corrected grasping force models, the parametric optimization of mechanism dimensions is conducted, which improves the load output performance of mechanism in the two-point grasping mode and the enveloped grasping mode comprehensively.RecurDyn simulation results show that, the maximum relative error between the corrected complete grasping force models and the simulation values is 7.62% in the two-point grasping mode and enveloped grasping mode, and the proposed optimization algorithm improves the two-point grasping force and comprehensive enveloped grasping force of mechanism effectively.The experimental results show that, the grasping force of optimal grasping mechanism is significantly improved, and the maximum relative error between the corrected complete grasping force models and the experimental values is 1.87%, which verifies the effectiveness of the grasping force modeling and optimization design.