Abstract: A 3-PPSR flexible parallel robot with high aspect ratio for micromanipulation is designed to achieve a greater workspace. It is driven by a piezoelectric motor, connected by flexible hinges with high aspect ratio, the deformation of which is in the millimeter range, suitable for large deformation. And, it has the advantages of simple structure, non-singular motion, no gap and high motion precision. Because the stiffness of the system directly affects the motion accuracy and the load bearing performance, firstly the mathematical model of flexible hinge is established through finite element method, according to the characteristics of the flexible hinge with high aspect ratio. Then, the flexible stiffness model of system is set up by using the method of integral stiffness and combining coordination equation with force balance equation. Finally, the theoretical stiffness model is compared with the finite element analysis based on ANSYS. The result analysis demonstrates that the stiffness model is valid, and matches with the motion characteristics of the proposed mechanism.